@ballbearian covered this in his build thread starting here. Member 66Sprint (who recently passed) came up with a nice solution to the over advance issue.
-
Don't overlook our Welcome Package, it contains many links to important and helpful information about functions at VHT like posting pictures and sending PMs (private messages), as well as finding the parts you need.
AD
1961 CB72 The Long and Winding Road
- Thread starter Pridanc
- Start date
crazypj
Veteran Member
- Joined
- Jun 5, 2020
- Total Posts
- 1,583
- Total likes
- 1,030
The centrifugal filter is actually much more efficient than paper one, particularly if you use more than 6K rpm.
There is a discussion about it on here somewhere
There is a discussion about it on here somewhere
Pridanc
Veteran Member
Hey crazypj,
Thanks for jumping in.
After all the time spent cleaning this little beast, and then reading up on centrifugal filters, I played a game of Roshambo to settle it as I was stuck.
Anyway there's no question a centrifuge is a super interesting way to keep the life blood clean but all said and done, I'm good with my choice here.
Stay well!
Thanks for jumping in.
After all the time spent cleaning this little beast, and then reading up on centrifugal filters, I played a game of Roshambo to settle it as I was stuck.
Anyway there's no question a centrifuge is a super interesting way to keep the life blood clean but all said and done, I'm good with my choice here.
Stay well!
crazypj
Veteran Member
- Joined
- Jun 5, 2020
- Total Posts
- 1,583
- Total likes
- 1,030
I had to look up Roshambo, never heard it before. 
ballbearian
Veteran Member
This is a great thread, really enjoying it. The work on cleaning the crank oilways and sludge traps in it were extra special.
The roll pin advance limiters must be holding up ok in mine so far.
The roll pin advance limiters must be holding up ok in mine so far.
Pridanc
Veteran Member
crazy, I only knew it because of my kids. When I grew up it was Rock-Paper-Scissors. You should have seen me trying to spell it. Thank gosh for the net, otherwise it would have been ugly.I had to look up Roshambo, never heard it before.
Pridanc
Veteran Member
#28
By now y'all know that as I leave the head and return to the bottom end, I can't imagine I'm not forgetting something so it'll be no surprise if I go back. If I do, I'll do my best to say I did in case anyone wants to see what googball thing I dropped.
Bottom end and gears.
Before jumping in, my brain has this tease of some little chicklet thing (in the red circle) that can be installed backwards as it can physically go back incorrectly, but am told the mechanism will not work properly or perhaps not as well as it would.. So I'm openly saying I think it is the little chicklet thing mentioned to me and is a part of the kick start mechanism. IF my brain serves me, you can put it in flipped (side to side, not end to end) and it will work but not well? Say I the expert here. As I do not remember if this is the "don't forget" bit that was mentioned to me, just make sure yours goes back together like this and you are covered.
No matter what, keep copious pictures as you take it apart and then put it all back the way you came. As mentioned, non of this is hard so just go slow and if something seems amiss, stop and think about it. Every piece is there for a reason and knowing its job also then means there is only one place it can go.
By now you know that once I've spent the time to get somewhere, like inside an old engine, I'm replacing all the parts that seem slightly too worn. Typically this is bearings, bushings and any seals. If you find parts not too worn in your opinion, you do not have to replace them but I'd replace the seals regardless. Regardless , this is your baby so the decision is yours. As I'm lazy. I tend to do the "out with the old" trick very often. So lets not mention this out-with-the-old to my wife as I rather enjoy being inside my old house. Deal?
Bearings, IMO, are good if not overly sloppy and roll without any glitch's, bumps, or complaints. Again mine felt ok and many passed my smell test, and I have a sensitive nose. One small example is this bush which was visibly worn in this circled area and although it was working at doing its job, it had to go IMO.
Once the lower half of the engine case was pulled of, it was time to clean and inspect. Old engines get nasty with age. OK, so do Old ppl like me.
We've discussed the bearings and bushes, but time to look hard at all those part that make up the transmission. Are the dogs on the gears good? Are the grooves in the shifting drum good? Is any part of the shift forks warn enough to impart slop? Some of this can impede function but equally bad, create imprecision when none was meant to be. In my case, this is a restoration and not just an exploration to catch what was getting long on tooth and then leaving it. A "resto" means making it new again. As I've spent more hours than I want to know exploring a resto, in many ways, is easier. Things that wear tend to have little chance of staying which means less time looking and agonizing. See? EZ-er...for me!
The Shift drum is at the very top. Looks like a rolling pin for small pizzas. Those curvy slots have some pins that ride in them, forcibly moving things around. When you operate the shift lever with your foot, you turn this drum which then moves the forks that select a gear. So look at the slots and the pin end of the bolts. All this is pointed out in purple.
In my experience forks tend to wear at the yellow circles. These can wear in more than just this area but this is typically the first area. Do they have to be perfect, well no, but those forks slide into a groove of two gears (one fork, one gear) as can be seen here above. Follow the blue lines. The half moon shape in the forks fit into the groove you see in the gear here. Just look for wear and if you think it too much, then phone-a-fren who's done this before, OR, look at a few pictures online. FleaBay typically has good pictures to help you decide.
Gears teeth should still have good form. Typically wear appears on one side of each tooth so if you see a side that no longer has the shape of the other side of the same tooth, time to think harder. And look at the dogs. That is the dogs the arrows point to below. (you can also see dogs on the gear above as another point of reference.)
Dogs are wear items but when these edges get too worn, you may want to replace the gear/gears. As you can see here these edges look sharp and precise. As they wear, these edges grow, as in the radius gets larger and less defined. If you look close, you can see that the sides of the dogs, lets call it their left and right side (not top or bottom?) are tapered in. They have a reverse cut which helps the dogs pull each other together under load. As the edges become rounded corners, there is less and less taper to grab to the dogs become less effective. Oh yes, the still work but shifting may need to be more authoritative with damage and age.
Before I leave this post, I want to mention my gear choices and why. This topic of to X or not to X is well documented. Nonetheless as a bum who's changed too many gears in quick change dog boxes for cars, I have gear charting stuff to take the gear ratio info and stare. These days this is not so innocent as it once was because I now drool. Not from a cool factor but just because. Hey, old dogs drool OK? Sad, I know.
I'm sure this is out there 100 times but what the heck, here it is again. And I've got numbers as well but a graph like this is generally all telling for me. If I need more info to help sway me, then I grab the numbers.
Forgive the blurriness as my computer and I were arguing and it won. However it sure seems to me to be clear enough to get the point across. Two charts are combined here.
One is the OE as delivered gear stack in this engine in all black. The chart with the purple bits is the famed X box. 1st gear and 4th gears are the same so share the same bit of black, but this displays
the new 2nd and 3rd gears and the change they bring in purple. Clearly, the X box has less rpm drop between the lower gears and in hind sight,
this may well be the right choice for many of y'all. But for me, a guy who doesn't care for stop-n-go traffic of a city, the OE box fits my bill for the
gentle rolling hills and curves I prefer. Top 3 gears are closer making it easier to keep the little buzzer on the boil. Like most everything here in the description of my journey, the choice is yours.
And even if you decide later you'd like to give the other stack a try, well step right up as you can! No need to buy any other parts. I will however toss out that this just might fall in the PITA range of things
to do on a Saturday afternoon.
Enjoy your weekend as I'm off to watch more of the LeMans 24. Talk later.
By now y'all know that as I leave the head and return to the bottom end, I can't imagine I'm not forgetting something so it'll be no surprise if I go back. If I do, I'll do my best to say I did in case anyone wants to see what googball thing I dropped.
Bottom end and gears.
Before jumping in, my brain has this tease of some little chicklet thing (in the red circle) that can be installed backwards as it can physically go back incorrectly, but am told the mechanism will not work properly or perhaps not as well as it would.. So I'm openly saying I think it is the little chicklet thing mentioned to me and is a part of the kick start mechanism. IF my brain serves me, you can put it in flipped (side to side, not end to end) and it will work but not well? Say I the expert here. As I do not remember if this is the "don't forget" bit that was mentioned to me, just make sure yours goes back together like this and you are covered.
No matter what, keep copious pictures as you take it apart and then put it all back the way you came. As mentioned, non of this is hard so just go slow and if something seems amiss, stop and think about it. Every piece is there for a reason and knowing its job also then means there is only one place it can go.
By now you know that once I've spent the time to get somewhere, like inside an old engine, I'm replacing all the parts that seem slightly too worn. Typically this is bearings, bushings and any seals. If you find parts not too worn in your opinion, you do not have to replace them but I'd replace the seals regardless. Regardless , this is your baby so the decision is yours. As I'm lazy. I tend to do the "out with the old" trick very often. So lets not mention this out-with-the-old to my wife as I rather enjoy being inside my old house. Deal?
Bearings, IMO, are good if not overly sloppy and roll without any glitch's, bumps, or complaints. Again mine felt ok and many passed my smell test, and I have a sensitive nose. One small example is this bush which was visibly worn in this circled area and although it was working at doing its job, it had to go IMO.
Once the lower half of the engine case was pulled of, it was time to clean and inspect. Old engines get nasty with age. OK, so do Old ppl like me.
We've discussed the bearings and bushes, but time to look hard at all those part that make up the transmission. Are the dogs on the gears good? Are the grooves in the shifting drum good? Is any part of the shift forks warn enough to impart slop? Some of this can impede function but equally bad, create imprecision when none was meant to be. In my case, this is a restoration and not just an exploration to catch what was getting long on tooth and then leaving it. A "resto" means making it new again. As I've spent more hours than I want to know exploring a resto, in many ways, is easier. Things that wear tend to have little chance of staying which means less time looking and agonizing. See? EZ-er...for me!
The Shift drum is at the very top. Looks like a rolling pin for small pizzas. Those curvy slots have some pins that ride in them, forcibly moving things around. When you operate the shift lever with your foot, you turn this drum which then moves the forks that select a gear. So look at the slots and the pin end of the bolts. All this is pointed out in purple.
In my experience forks tend to wear at the yellow circles. These can wear in more than just this area but this is typically the first area. Do they have to be perfect, well no, but those forks slide into a groove of two gears (one fork, one gear) as can be seen here above. Follow the blue lines. The half moon shape in the forks fit into the groove you see in the gear here. Just look for wear and if you think it too much, then phone-a-fren who's done this before, OR, look at a few pictures online. FleaBay typically has good pictures to help you decide.
Gears teeth should still have good form. Typically wear appears on one side of each tooth so if you see a side that no longer has the shape of the other side of the same tooth, time to think harder. And look at the dogs. That is the dogs the arrows point to below. (you can also see dogs on the gear above as another point of reference.)
Dogs are wear items but when these edges get too worn, you may want to replace the gear/gears. As you can see here these edges look sharp and precise. As they wear, these edges grow, as in the radius gets larger and less defined. If you look close, you can see that the sides of the dogs, lets call it their left and right side (not top or bottom?) are tapered in. They have a reverse cut which helps the dogs pull each other together under load. As the edges become rounded corners, there is less and less taper to grab to the dogs become less effective. Oh yes, the still work but shifting may need to be more authoritative with damage and age.Before I leave this post, I want to mention my gear choices and why. This topic of to X or not to X is well documented. Nonetheless as a bum who's changed too many gears in quick change dog boxes for cars, I have gear charting stuff to take the gear ratio info and stare. These days this is not so innocent as it once was because I now drool. Not from a cool factor but just because. Hey, old dogs drool OK? Sad, I know.
I'm sure this is out there 100 times but what the heck, here it is again. And I've got numbers as well but a graph like this is generally all telling for me. If I need more info to help sway me, then I grab the numbers.
Forgive the blurriness as my computer and I were arguing and it won. However it sure seems to me to be clear enough to get the point across. Two charts are combined here.
One is the OE as delivered gear stack in this engine in all black. The chart with the purple bits is the famed X box. 1st gear and 4th gears are the same so share the same bit of black, but this displays
the new 2nd and 3rd gears and the change they bring in purple. Clearly, the X box has less rpm drop between the lower gears and in hind sight,
this may well be the right choice for many of y'all. But for me, a guy who doesn't care for stop-n-go traffic of a city, the OE box fits my bill for the
gentle rolling hills and curves I prefer. Top 3 gears are closer making it easier to keep the little buzzer on the boil. Like most everything here in the description of my journey, the choice is yours.
And even if you decide later you'd like to give the other stack a try, well step right up as you can! No need to buy any other parts. I will however toss out that this just might fall in the PITA range of things
to do on a Saturday afternoon.
Enjoy your weekend as I'm off to watch more of the LeMans 24. Talk later.
Last edited:
crazypj
Veteran Member
- Joined
- Jun 5, 2020
- Total Posts
- 1,583
- Total likes
- 1,030
Suzuki used very similar sprag mechanism for decades on gear change drum. If you asked me which way it went I wouldn't remember without looking at it.
Suzuki had a left and right with offset slot for spring.
Those transmission gears look brand new?
Didn't Honda make a close ratio set for the road race conversion? (and maybe a wide ratio/extra low first gear for desert racers?)
CB72/77 is one of the few motors I've never had in pieces but as the first 'real' bike I ever fell off has a special memory for me. (about 55 years ago)
Suzuki had a left and right with offset slot for spring.
Those transmission gears look brand new?
Didn't Honda make a close ratio set for the road race conversion? (and maybe a wide ratio/extra low first gear for desert racers?)
CB72/77 is one of the few motors I've never had in pieces but as the first 'real' bike I ever fell off has a special memory for me. (about 55 years ago)
Pridanc
Veteran Member
You are now punching way over my head. By that I mean there could well be a race sets of ratios and there might even be a 5 speed but those are just whispers to me as I knew that none of that was on my radar even if cool so I did no digging.
And yes, those two gear are pictures off of Fleabay. You don't think I had the foresight to take pictures of mine did you? Sad when I set out to take more pictures than you possibly could. Clearly I was off my meds that day. But good eye, as yes. those are spanking new as examples but if you look closely to the one picture of it assembled prior to coming all apart, the dogs look good and were.
Stay well.
Last edited:
Pridanc
Veteran Member
#29
Lets finish up the engine. I realize that for many, rebuilding an engine can be daunting but IMO it needn't be.
If you follow these suggestions , it will be hard to screw up but above all don't doubt yourself! Nothing here is rocket science so take it a step at a time. Read up on the task ahead so when you are doing it, most of it won't be completely foreign to you.
1) Get hold of the shop manual.
I got this manual inside a bunch of info I purchased from Bill Silver. Manuals aside, there is so much interesting info separate from manual I got from BIll I still go back and read them to see what I missed. Simply marvelous information.
2) Make sure you have a parts book. (got it with the Shop manual etc) I've seen some that have too few pages so watch out for those. Bill's is complete for this bike. There are some type-O's in the book but your eyes will not lead you astray. I'd bet all this info can be found here on the forum.
3) Take copious pictures as you disassemble so that if in doubt, you can go to your detailed and plentiful pictures. Do not use me as an example as clearly I didn't follow my own mantra.
4) If / when taking things apart that are known to have small bits that can fall at the most inopportune times, give yourself a safety net. If I have a large area to cover, I use old towels laid down because nothing bounces after hitting a towel so bits wont' get lost. Most common for me is a very large cookie pan with said towel. No matter what you choose, just think about what you'll do IF (when) something sneaks out on its own. BTW , once you know how this engine, or anything your are working on goes together, you will forego the towels. It a process.
5) You can always "phone a friend" aka text or email "those in the know". This very forum as one of those friends so use it. People really like to help so take advantage of that.
As you may now know, the CB72 / 77 crankshafts are made up of 5 pieces and their assembly takes a press and great patience. Think about it. all the pieces need to go together such that all sections are the correct length (and by then, naturally, the OA length of the crank would be in spec), that all parts are "square" to each other, IE, the crank and parts are flat, or perpendicular to each other where it matters and finally, that each part is rotationally in the exact spot. Oh, and DO NOT forget the rods, their needle bearings and cages. I promise that if you did? You'd be so ready to cry.
BTW, it takes lots of pressure to get these parts to become one again. If memory serves 7-10 tons. The moaning of the press is indicative that it is having to work. A lot. My brain hurts to even contemplate doing this. Thankfully my man Tim Miller was well versed. Even if I had the capability to do this, that is a press that was in the 15-20 ton range, not sure I would have attempted it myself. A lot of that is my patience level and nor do I need to learn on the only crankshaft I have. Yes, I am happy to admit that I am a slacker
Old news. Pictures, what pictures? How I don't have a pic of the crank with rods just laying on the bench is beyond me. Sorry.
Now we are going to reverse the steps taken do dismantle the engine. As I haven't done a CB72 before, I'm not sure is there is a huge reason for a specific installation order of these large parts. Just take your time.
Anyway, drop the built-up crankshaft back in making absolutely certain that the bearings fit over their pins in the crankcase. I'm not sure it really matters since this engine had a pin pushed into the case without engaging the bearing as intended ,yet there was no noticeable damage at disassembly. The pins are there for a reason however so there's that. Indeed, this bearing survived and you can see here where this pin got pushed back up followed with some oil-resistant epoxy placed on the pin's back-side hole hoping to keep it in place. Yes, the crank was laid back into the case carefully making sure the pins were in place and that the bearings were all happy.
The picture below sucks (by now, no such a surprise right?) but is an attempt to better show what I'm talking about here. The Red arrow points to the pin that was pushed into the case and was not engaged in the bearing. Angle of the picture doesn't show that the pin is flush with the surface. The green arrow shows a pin still sitting proud as they all are meant to be. And then the epoxy repair to the hole after the pin was pushed back up into place.
Next the gear stacks and as you are doing this, watch that the three seals are nice and happy. One on the crankshaft, one on each of the gearbox shafts. There are only seals on one side of each shaft. The other side of the shafts, the clutch side, all live in oil so no oil seal needed. If the seals end up cocked, this will be as my Dutch friend says: " Not so very good". Truth is, I'm not sure I've ever had a seal **** itself when being trapped by two crankcase halves. Just look at them and if they look close to vertical, you are good. The halves clamping together will have them behave.
After a final clean of the mating surfaces of the two crankcase halves, apply your choice of sealant to the surface staring up at you. (not both surfaces) Like cards its "thin to win" as you want to avoid extra slop. As an old air cooled Porsche guy, I used something called Drei-Bond and or Loctite 574 but don't recall what was used here. But don't panic as there are several great options other than my go to sealants mentioned above as all are excellent: Hondabond (or its equivalents: ThreeBond 1184/1194, Yamabond, or Permatex Moto-Seal.) The only product here I've not used is Permatex Moto-Seal but lets face it, Permatex has an outstanding reputation so again, my thoughts are that each of these will easily get the job done.
Now Drop the Bottom half of the crankcase onto this bunch of bits and voila...we are getting there.
Below is Honda's suggested torqueing sequence for the fasteners of this lower crankcase. Do a search here on the forum as there are some great suggestions that have a suggestions of a different tightening sequence. Of course, you can't go wrong doing it the way Honda did back in the day so if you follow this guide, you are covered regardless. Torques for these is a bit vague so do some spelunking. Again, this forum then "around", as the crankcase torque specs are one of those areas where many points back to general Honda practices (at times I'm not sure what that is) because the original factory manuals are IMO surprisingly vague on the smaller bolts. As I'm a big old chicken, I tend to go slightly under or choose a median value. This I tend to default to a diameter-based approach so M8s are around 15 ft-lbs, M6s 7–10 ft-lbs, always staged in three steps. 1) snug, 2) 50% and 3) use the listed torques mentioned here or what you feel best per forums or others with real knowledge of these. I do not have any hard knowledge but would not hesitate to use the numbers I list. Let your conscience be your guide.
Now you can start adding all the bits that came off prior to splitting the case. And while you are here, don't forget to verify placement and function of the shifting mechanisms. If after full assembly you feel you got it wrong you can always go back and look at it but you'll have to drop the outside the clutch cover which holds oil so be ready for a tsunami of oil. Moral here is to work the shift mechanism before moving on as in change gears etc. Whilst manually changing gears, now might be a great time to install your neutral gear indicator sensor to test on the bench which you may recall lives very near the chain drive sprocket on the right side of the engine? This is a simple on-off switch which activates a lamp in the Nacelle when in neutral.
Here is a picture of the neutral switch installed and regret that the only pic I have is this "pre clean" picture. Nasty.
Gear Selector mechanism. Resplendent in dirt. Dang it all as I've clearly misplaced some photos as I'm not seeing my clean bits. Seriously though, work this and watch how it does its job. Very cool if you ask me. When you are working it, you may have to "jog" the chain sprocket since the engine isn't running so gears are just sitting there.
I'll drop a few more pictures of the before the bottom of the crankcase was dropped back on. I'm so irritated with my lack of pictures at the moment but spilt milk and all... you know the rest.
Reminder here. GREEN words indicate I came back and added something. It is lame here, but I've no doubt I'll be going back and adding sections I forgot, then it will be a sea of green.
Later
Lets finish up the engine. I realize that for many, rebuilding an engine can be daunting but IMO it needn't be.
If you follow these suggestions , it will be hard to screw up but above all don't doubt yourself! Nothing here is rocket science so take it a step at a time. Read up on the task ahead so when you are doing it, most of it won't be completely foreign to you.
1) Get hold of the shop manual.
I got this manual inside a bunch of info I purchased from Bill Silver. Manuals aside, there is so much interesting info separate from manual I got from BIll I still go back and read them to see what I missed. Simply marvelous information.
2) Make sure you have a parts book. (got it with the Shop manual etc) I've seen some that have too few pages so watch out for those. Bill's is complete for this bike. There are some type-O's in the book but your eyes will not lead you astray. I'd bet all this info can be found here on the forum.
3) Take copious pictures as you disassemble so that if in doubt, you can go to your detailed and plentiful pictures. Do not use me as an example as clearly I didn't follow my own mantra.
4) If / when taking things apart that are known to have small bits that can fall at the most inopportune times, give yourself a safety net. If I have a large area to cover, I use old towels laid down because nothing bounces after hitting a towel so bits wont' get lost. Most common for me is a very large cookie pan with said towel. No matter what you choose, just think about what you'll do IF (when) something sneaks out on its own. BTW , once you know how this engine, or anything your are working on goes together, you will forego the towels. It a process.
5) You can always "phone a friend" aka text or email "those in the know". This very forum as one of those friends so use it. People really like to help so take advantage of that.
As you may now know, the CB72 / 77 crankshafts are made up of 5 pieces and their assembly takes a press and great patience. Think about it. all the pieces need to go together such that all sections are the correct length (and by then, naturally, the OA length of the crank would be in spec), that all parts are "square" to each other, IE, the crank and parts are flat, or perpendicular to each other where it matters and finally, that each part is rotationally in the exact spot. Oh, and DO NOT forget the rods, their needle bearings and cages. I promise that if you did? You'd be so ready to cry.
BTW, it takes lots of pressure to get these parts to become one again. If memory serves 7-10 tons. The moaning of the press is indicative that it is having to work. A lot. My brain hurts to even contemplate doing this. Thankfully my man Tim Miller was well versed. Even if I had the capability to do this, that is a press that was in the 15-20 ton range, not sure I would have attempted it myself. A lot of that is my patience level and nor do I need to learn on the only crankshaft I have. Yes, I am happy to admit that I am a slacker
Old news. Pictures, what pictures? How I don't have a pic of the crank with rods just laying on the bench is beyond me. Sorry.
Now we are going to reverse the steps taken do dismantle the engine. As I haven't done a CB72 before, I'm not sure is there is a huge reason for a specific installation order of these large parts. Just take your time.
Anyway, drop the built-up crankshaft back in making absolutely certain that the bearings fit over their pins in the crankcase. I'm not sure it really matters since this engine had a pin pushed into the case without engaging the bearing as intended ,yet there was no noticeable damage at disassembly. The pins are there for a reason however so there's that. Indeed, this bearing survived and you can see here where this pin got pushed back up followed with some oil-resistant epoxy placed on the pin's back-side hole hoping to keep it in place. Yes, the crank was laid back into the case carefully making sure the pins were in place and that the bearings were all happy.
The picture below sucks (by now, no such a surprise right?) but is an attempt to better show what I'm talking about here. The Red arrow points to the pin that was pushed into the case and was not engaged in the bearing. Angle of the picture doesn't show that the pin is flush with the surface. The green arrow shows a pin still sitting proud as they all are meant to be. And then the epoxy repair to the hole after the pin was pushed back up into place.
Next the gear stacks and as you are doing this, watch that the three seals are nice and happy. One on the crankshaft, one on each of the gearbox shafts. There are only seals on one side of each shaft. The other side of the shafts, the clutch side, all live in oil so no oil seal needed. If the seals end up cocked, this will be as my Dutch friend says: " Not so very good". Truth is, I'm not sure I've ever had a seal **** itself when being trapped by two crankcase halves. Just look at them and if they look close to vertical, you are good. The halves clamping together will have them behave.
After a final clean of the mating surfaces of the two crankcase halves, apply your choice of sealant to the surface staring up at you. (not both surfaces) Like cards its "thin to win" as you want to avoid extra slop. As an old air cooled Porsche guy, I used something called Drei-Bond and or Loctite 574 but don't recall what was used here. But don't panic as there are several great options other than my go to sealants mentioned above as all are excellent: Hondabond (or its equivalents: ThreeBond 1184/1194, Yamabond, or Permatex Moto-Seal.) The only product here I've not used is Permatex Moto-Seal but lets face it, Permatex has an outstanding reputation so again, my thoughts are that each of these will easily get the job done.
Now Drop the Bottom half of the crankcase onto this bunch of bits and voila...we are getting there.
Below is Honda's suggested torqueing sequence for the fasteners of this lower crankcase. Do a search here on the forum as there are some great suggestions that have a suggestions of a different tightening sequence. Of course, you can't go wrong doing it the way Honda did back in the day so if you follow this guide, you are covered regardless. Torques for these is a bit vague so do some spelunking. Again, this forum then "around", as the crankcase torque specs are one of those areas where many points back to general Honda practices (at times I'm not sure what that is) because the original factory manuals are IMO surprisingly vague on the smaller bolts. As I'm a big old chicken, I tend to go slightly under or choose a median value. This I tend to default to a diameter-based approach so M8s are around 15 ft-lbs, M6s 7–10 ft-lbs, always staged in three steps. 1) snug, 2) 50% and 3) use the listed torques mentioned here or what you feel best per forums or others with real knowledge of these. I do not have any hard knowledge but would not hesitate to use the numbers I list. Let your conscience be your guide.
Now you can start adding all the bits that came off prior to splitting the case. And while you are here, don't forget to verify placement and function of the shifting mechanisms. If after full assembly you feel you got it wrong you can always go back and look at it but you'll have to drop the outside the clutch cover which holds oil so be ready for a tsunami of oil. Moral here is to work the shift mechanism before moving on as in change gears etc. Whilst manually changing gears, now might be a great time to install your neutral gear indicator sensor to test on the bench which you may recall lives very near the chain drive sprocket on the right side of the engine? This is a simple on-off switch which activates a lamp in the Nacelle when in neutral.
Here is a picture of the neutral switch installed and regret that the only pic I have is this "pre clean" picture. Nasty.
Gear Selector mechanism. Resplendent in dirt. Dang it all as I've clearly misplaced some photos as I'm not seeing my clean bits. Seriously though, work this and watch how it does its job. Very cool if you ask me. When you are working it, you may have to "jog" the chain sprocket since the engine isn't running so gears are just sitting there.
I'll drop a few more pictures of the before the bottom of the crankcase was dropped back on. I'm so irritated with my lack of pictures at the moment but spilt milk and all... you know the rest.
Reminder here. GREEN words indicate I came back and added something. It is lame here, but I've no doubt I'll be going back and adding sections I forgot, then it will be a sea of green.
Later
Attachments
Last edited:
That looks pretty clean to me. My C77 selector was in a much more abused state lol
Pridanc
Veteran Member
#30
More engine stuff.
Not that it matters to 99.99% of us, but thought I'd mention that through the years, and for various reasons only known by Honda (not a slam, just me talking) our Type I engines are considered the 180° engines vs. the Type 2 being considered a 360°. This has to do with the crankshaft layout. These choices affect several things in the engine from power delivery to balance and more. See link below for some education.
Those in the know, most definitely not me, have the knowledge and only have to glance at the bike and can say what type engine that bike uses. I have to look at the points cover Rt side of the engine. You know, the cheat sheet.
The engine in this bike is a Type 1 180 degree engine with the "whack a mole" pistons. I don't have an open picture of the Type 2 but you can see the difference here.
I was going to pontificate about "why this firing order over another" but know that a far better explaination sits with much smarter people than I so follow this link to a gent well worth a listen too. In this case he discusses the various differences in vertical twin firing orders which encompasses the Honda Type I and Type 2 by default. His presentations are such that even this cave man gets it. And besides this video, he has many engine related videos you will enjoy, I promise.
Straightened some fins, cleaned 'er on up. OK, lets admit it is cleaner but the backgrounds affect the shine here too.
Couple of more next entry.
More engine stuff.
Not that it matters to 99.99% of us, but thought I'd mention that through the years, and for various reasons only known by Honda (not a slam, just me talking) our Type I engines are considered the 180° engines vs. the Type 2 being considered a 360°. This has to do with the crankshaft layout. These choices affect several things in the engine from power delivery to balance and more. See link below for some education.
Those in the know, most definitely not me, have the knowledge and only have to glance at the bike and can say what type engine that bike uses. I have to look at the points cover Rt side of the engine. You know, the cheat sheet.
The engine in this bike is a Type 1 180 degree engine with the "whack a mole" pistons. I don't have an open picture of the Type 2 but you can see the difference here.
I was going to pontificate about "why this firing order over another" but know that a far better explaination sits with much smarter people than I so follow this link to a gent well worth a listen too. In this case he discusses the various differences in vertical twin firing orders which encompasses the Honda Type I and Type 2 by default. His presentations are such that even this cave man gets it. And besides this video, he has many engine related videos you will enjoy, I promise.
Straightened some fins, cleaned 'er on up. OK, lets admit it is cleaner but the backgrounds affect the shine here too.
Couple of more next entry.
Pridanc
Veteran Member
#31
Couldn't stop and leave you hanging.
Baby steppin'.
Later...!
Couldn't stop and leave you hanging.
Baby steppin'.
Later...!
Looks really good. I see you used 3 base gaskets, was this because of having the cylinder decked or were the piston were a little higher?
Greybeard70
Member
Very educational video, I found it quite interesting. I have watched other videos by the same guy and learn from them also.
Pridanc
Veteran Member
Yes, at some point the head was cut 0.030" which gave pause to consider our goals here. At every turn, OE like and long life so several things transpired
1) To make block flat and perpendicular, as you've seen the top was cut.
2) Between the head, and the block, the cam timing would now be out with no way to get it back without creating / installing a sprocket that permits timing adjustment like this from Cappellini Moto
the 4 slots allow the bolts to slide unlike the stock gear. This gear is rarely seen without the ignition advancing weights / springs.
3) Although compression wasn't a giant concern, it was a consideration
Those three things combined made the decision to put all the bits back to where the belonged, relative the crankshaft, a no brainer.
Last edited by a moderator:
Pridanc
Veteran Member
#32
I was going to discuss carbs later by why not now as it is an engine ancillary right? And we are kind of, sort of there yes?
I’ve messed with many a carb in my life time ( which does not make me an expert) but because of that, jumping into them does not intimidate me and nor should it you.
Luckily the Keihin Power Jet carbs found on this bike as well as the CB77, is not complicated. The only real difference I can see between the two bikes of this year, are the bore size of the carbs. A Keihin PW22 for the CB72 like this one, and a PW 26 for the 77. Of all the carbs I ever messed with, only the “rack-o-lamb” Honda CBX carbs were what I’d call a pain in the backside. And even then, really only a PITA because of all the added bits these carbs have not to mention the need to keep track of the idle-up feature of the choke mechanism. As we’ve discussed on the engine here, take lots of pictures and have a parts manual beside you. It all goes back together the same as it came apart. I keep a selection of hammers near at all times.
No matter what, IMO, the most important thing you can do is to clean the heck out of them. Each and every part. Prior to actual cleaning these were stripped to the bones with each part catalogued. Cleanliness is paramount to good function and future tunability of your carbs moving forward so spare nothing here. I used solvents, ultrasonic cleaning, fine sanding medium by hand (like 3m Scotch Brite) and some Vapor blasting to finish the outside of the bodies. As I’m chicken about the possibility of getting blasting medium into the passageways, I was very careful about that. Point being, no one thing was used to get them into shape in my case.
This is before disassembly. 
Ironically, I found nothing odd about these carbs internally other than one float bowl had rotted out so was full of holes. I’m told these can be found but none seem available when I look. I know I can have new ones printed as I went down that road but in the interim, I chose fuel proof epoxy.
I ended up with some marine stuff I tested for about a year and still seems OK. I sealed the leaking bowl internally effectively hiding the damage but beyond this. You have to look hard to find the repaired bowl from the outside. Otherwise the only thing I found to be an issue were the float heights.
Left, before clean and repair. Right, cleaned but not yet repaired. Today, it is hard to tell this was ever wonded.
I had to straighten part of the choke lever. As we go through the bike reassembly, this becomes a recurring them. Bend, then re-plate.
Each jet/part should be clean, each hole in every jet or tube should have clear unobstructed passage. Once you are convinced all that is good, and making sure your eyes are covered as a precaution please, go back and squirt carb cleaner through every passage making sure the cleaner comes out on all the places it should. Now blow each passage out with compressed air. It is imperative that the passages are clean. If after close inspection you still have doubt about any jet (or part) , buy new! I’m sure there are some fantastic jet copies out there but for me, the few extra bucks of the real thing give me a greater level of comfort of the new jets being the same as the day this bike was built. Paranoid much? LOL
There are only a few parts that can actually wear out over time and of those, the reality is for just the needle and seat and maybe, just maybe, the throttle slide itself. If you choose to keep the needle and seat you have, test them first. Easiest way for me to test is to install them back into the carb body with their floats and then blow through the fuel line inlet using your mouth as you don’t need much pressure here. The needle and seat only have to stop gravity fed fuel which ends up being very little pressure at the seat. With the float hanging down exerting no pressure on the needle at all, the air from your lungs should flow freely through the needle and seat. Now tilt the carb until the needle is pushed into its seat. Air flow should stop.
If you find your throttle slides have too much wear, which is possible but no common, replace them. Reason being that worn slides pass too much air around themselves creating havoc with the fueling system of the carburetor. I promise that if this is the case, you’ll go crazy trying to tune the idle, off idle, and general low speed running if the engine.
There are times I’ve found that you can eye-ball the float heights with a ruler and your Eye-Ometer. However there are times when, and I feel these baby Hondas with the round floats are it, you might want to purchase or make a tool to more accurately measure the float height. When you have a small bore engine trying to use a slightly large bore carb, low engine RPM doesn’t send the carb good strong signals so confusion can reign. I'm not sure why there are two styles of floats (and float bowls) but mine are the round type so making a tool makes measuring the float height easier and way more accurate. If the floats have flat sides, then this is easily achieved with out modifying your Vernier as I did to get the task done.
The CB72 floats are to be set at or dang close to 26.5mm
Notice the bulbous sides of these floats above? They stop you from using a plane old vernier if not for the extension seen added here. Right hand drawing shows we are measuring h from the surface of the gasket face flat of the body to the top of the float.
Commercial version and I'm sure there are others out there. This one can be found at 4into1.com
As you’ve just cleaned the carbs and they are in hand on the bench, make sure your idle speed screws are all the way out so that the slides can sit at their rock bottom in the carb body. Leave the screw turned out for now and continue assembly.
Jumping ahead to speak more about floats, running the engine for the first time was wonderful except for throttle response. The thing was lean. Jerking the carbs back off and the first thing I checked were the float heights. Sheesh but I must have been coming off of an all-nighter when I first set the floats on the bench because they were off. As in two mm or so. Hard to believe but I’m thinking the gaskets were in place (a no-no and I know better) Oddly when you stand back and think what the heck, how does a few mm mater? Well, it really does most particularly noticeable right off idle as the carb is doing its best to get the engine to pick up revs and then to draw the middle and high speed systems online in an effort to give the engine the fuel it needs at the correct time. If the fuel is too low in the bowl, it take more time and more pull to get the fuel out of the bowl and into the system to be used. Time is the issue here. The engine needs fuel when it needs it, not later.
When looking over the internal parts, do this for the floats as well. When they are in your hand, shake them. Listen for sloshing fuel. If you hear or feel any of that, replace the offending float. Note and as hinted, for some crazy reason, there are two types of floats for these carbs so snag the style you have.
Between us? Having spent some years using electronic fuel injection, I smilingly call a carburetor a “controlled leak”. Carbs are dead simple and in a pinch, I prefer them as it is hard to get one to fail but boy howdy can they be ornery to tune at times. Don’t forget that Honda and Keihin have done the heavy lifting here so all we need to do is to put things, like float levels, back where they belong all nice and clean like.
After the carbs were on the bike, I fed some fuel to it and the bike fired up almost instantly. BTW, hanging a small fuel container nearby gives you far greater access to the carbs just in case. You know, in case its best to remove them again. The CB’s fuel tank hides a lot even though you can still work and tune with the OE tank in place. As you may recall, we set the carb slide as low as they’d go so when you fire the engine, you will have to hold the throttle up a bit whilst allowing time for the engine to warm. A warm engine prefers a slightly different “tune” than a cold one so don’t rush it. Last I checked, the engines are nice and warm when we ride them right?
Back to the basics:
1) check, and set if needed, valve clearance.
2) check, and set if necessary, the ignition timing. Once those are known and you are happy, proceed with the carb!
4) Now with the carbs bolted onto the engine, with good O rings on carb and manifold, verify your needle position one more time is there is any concern. So long as they are the same, proceed. In my case, I have my 22402 needles at second richest setting.
As can be seen here, my clip is in the slot position of the red arrow which raises the needles up in the slide to the second highest slot. In my case, I might even try the needle as high as it will go (last slot to the right of the arrow) but I’m getting ahead of myself. Needle height is a quick and easy change.
Once both slides are in, now it is time to mess with the throttle cables and how the slides respond to the twist of your wrist. (And yes, Keith Code’s books called A Twist of the Wrist are well worth the read) The goal here is to have both slides lift together. This is easy to do using your hand to touch the slides as you gently twist the throttle grip.
To get both slides to raise together, simply go to the adjuster on the carb that is not moving up when the other one does! Won’t take a lot, and before you know it, both slides move at the same time when opening the throttle.
The small screwdriver at the top of the pict is touching the adjuster. Raising the adjuster forces the carb slide to raise earlier because you've removed a bit of slack. Again, this rarely take a lot of adjustment.
Now the fun part. Once the engine is finally warm, turn in the idle speed screws (brass screw as seen above which looks like the cable luber is pointing to) until the engine is idling about where it ought to be. The manual says below 1000 rpm but me, I like a little more. Make sure you have raised the slides by their screws equally for this first swing at it until you can let go of the throttle and the engine will idle by itself.
Now you need to "balance" the carbs. That means that each cylinder is doing roughly the same work. There are tools to really get this close but you can come dang close yourself without the tools by feeling for equal exhaust pulsing or by the sound of using a 3/4” tube in your ear held at right angles to the carb throat. Like the feeling exhaust pulses, adjust carbs to provide the same sound from each carb. I swear, works well.
Tried to find the "stick" guy again to give him a shout out but of course....What Guy? Kudos to him.
On the left, the commercially available Uni-Syn. Works well, super easy to use. Just place and hold it onto the front opening of the carb and watch the little red indicator move. The goal is to make the red indicator be at the same level of that vertical clear tube for each carb. Now on the right, this is something new to me which I found whilst looking around I saw this and LOVE its simplicity though I’ve never tried it. You use a couple of sticks stuck into each carb levered under the open leading edge of the slide. As you move the slide up or down, the sticks move up and down. When sticks are at the same level, you are golden. Again, I’ve never used it but love the idea. Between the tubes in my ears, tools like the Uni-Syn or sticks along with the ability to feel the exhaust pulsing, I’m covered. You will be too.
Once you have an acceptable idle all “synched up”, now mess with your idle mixture screws. Again, some brass looking screws seen in the GREEN circle. These are angled up slightly. The Red circle shows the engine speed adjuster.
This little baby in the green circle adjusts the air/fuel mixture at idle and can raise and lower the RPM. Most people suggest turning it in or out to find the highest RPM which I do at times but often once I've found that sweet spot, I then turn the screw back in 1/8th to 1/4 turn. (this is richer). This will most likely lose you a few rpm but often I find the gains of off idle response is a worth while trade. Unlike most cars and many motorcycles, there is no accelerator pump to help the carb/engine through this tough area of carburation. YMMV so give it a whirl and settle on what works best for you.
Once you are happy with the mixture, you will most likely want to go back and set the idle speed to what you want which is where you may have been initially. Make sure you adjust the idle speed screws equally but feel free to re-visit the synching thing if you feel you messed it up. Remember? Ear, Vacuum, Sticks, exhaust pulsing, all quick and simple to do.
Now, shut the engine down and with your hand, check that the slides still move together. Very often you’ll find that this has changed because your idle speed screw is holding one slide higher than it did when we started. (Don't forget the slides were sitting on the floor of the carb body when we began) Changing the idles screws typically raises one slide higher than the next putting cable slack into that side. So like before, just take the slack out again with the adjuster on top of the carb. This can be a bit of a tap dance but no matter what, it is all very easy.
OK, I'm toast for now so....Later!
PS, if someone has a nice float bowl no longer wanted....feel free to reach out. I'm trusting the Epoxy but there's always a but... TY
I was going to discuss carbs later by why not now as it is an engine ancillary right? And we are kind of, sort of there yes?
I’ve messed with many a carb in my life time ( which does not make me an expert) but because of that, jumping into them does not intimidate me and nor should it you.
Luckily the Keihin Power Jet carbs found on this bike as well as the CB77, is not complicated. The only real difference I can see between the two bikes of this year, are the bore size of the carbs. A Keihin PW22 for the CB72 like this one, and a PW 26 for the 77. Of all the carbs I ever messed with, only the “rack-o-lamb” Honda CBX carbs were what I’d call a pain in the backside. And even then, really only a PITA because of all the added bits these carbs have not to mention the need to keep track of the idle-up feature of the choke mechanism. As we’ve discussed on the engine here, take lots of pictures and have a parts manual beside you. It all goes back together the same as it came apart. I keep a selection of hammers near at all times.
No matter what, IMO, the most important thing you can do is to clean the heck out of them. Each and every part. Prior to actual cleaning these were stripped to the bones with each part catalogued. Cleanliness is paramount to good function and future tunability of your carbs moving forward so spare nothing here. I used solvents, ultrasonic cleaning, fine sanding medium by hand (like 3m Scotch Brite) and some Vapor blasting to finish the outside of the bodies. As I’m chicken about the possibility of getting blasting medium into the passageways, I was very careful about that. Point being, no one thing was used to get them into shape in my case.
This is before disassembly. Ironically, I found nothing odd about these carbs internally other than one float bowl had rotted out so was full of holes. I’m told these can be found but none seem available when I look. I know I can have new ones printed as I went down that road but in the interim, I chose fuel proof epoxy.
I ended up with some marine stuff I tested for about a year and still seems OK. I sealed the leaking bowl internally effectively hiding the damage but beyond this. You have to look hard to find the repaired bowl from the outside. Otherwise the only thing I found to be an issue were the float heights.
Left, before clean and repair. Right, cleaned but not yet repaired. Today, it is hard to tell this was ever wonded.
I had to straighten part of the choke lever. As we go through the bike reassembly, this becomes a recurring them. Bend, then re-plate.
Each jet/part should be clean, each hole in every jet or tube should have clear unobstructed passage. Once you are convinced all that is good, and making sure your eyes are covered as a precaution please, go back and squirt carb cleaner through every passage making sure the cleaner comes out on all the places it should. Now blow each passage out with compressed air. It is imperative that the passages are clean. If after close inspection you still have doubt about any jet (or part) , buy new! I’m sure there are some fantastic jet copies out there but for me, the few extra bucks of the real thing give me a greater level of comfort of the new jets being the same as the day this bike was built. Paranoid much? LOL
There are only a few parts that can actually wear out over time and of those, the reality is for just the needle and seat and maybe, just maybe, the throttle slide itself. If you choose to keep the needle and seat you have, test them first. Easiest way for me to test is to install them back into the carb body with their floats and then blow through the fuel line inlet using your mouth as you don’t need much pressure here. The needle and seat only have to stop gravity fed fuel which ends up being very little pressure at the seat. With the float hanging down exerting no pressure on the needle at all, the air from your lungs should flow freely through the needle and seat. Now tilt the carb until the needle is pushed into its seat. Air flow should stop.
If you find your throttle slides have too much wear, which is possible but no common, replace them. Reason being that worn slides pass too much air around themselves creating havoc with the fueling system of the carburetor. I promise that if this is the case, you’ll go crazy trying to tune the idle, off idle, and general low speed running if the engine.
There are times I’ve found that you can eye-ball the float heights with a ruler and your Eye-Ometer. However there are times when, and I feel these baby Hondas with the round floats are it, you might want to purchase or make a tool to more accurately measure the float height. When you have a small bore engine trying to use a slightly large bore carb, low engine RPM doesn’t send the carb good strong signals so confusion can reign. I'm not sure why there are two styles of floats (and float bowls) but mine are the round type so making a tool makes measuring the float height easier and way more accurate. If the floats have flat sides, then this is easily achieved with out modifying your Vernier as I did to get the task done.
The CB72 floats are to be set at or dang close to 26.5mm
Notice the bulbous sides of these floats above? They stop you from using a plane old vernier if not for the extension seen added here. Right hand drawing shows we are measuring h from the surface of the gasket face flat of the body to the top of the float.
Commercial version and I'm sure there are others out there. This one can be found at 4into1.com
As you’ve just cleaned the carbs and they are in hand on the bench, make sure your idle speed screws are all the way out so that the slides can sit at their rock bottom in the carb body. Leave the screw turned out for now and continue assembly.
Jumping ahead to speak more about floats, running the engine for the first time was wonderful except for throttle response. The thing was lean. Jerking the carbs back off and the first thing I checked were the float heights. Sheesh but I must have been coming off of an all-nighter when I first set the floats on the bench because they were off. As in two mm or so. Hard to believe but I’m thinking the gaskets were in place (a no-no and I know better) Oddly when you stand back and think what the heck, how does a few mm mater? Well, it really does most particularly noticeable right off idle as the carb is doing its best to get the engine to pick up revs and then to draw the middle and high speed systems online in an effort to give the engine the fuel it needs at the correct time. If the fuel is too low in the bowl, it take more time and more pull to get the fuel out of the bowl and into the system to be used. Time is the issue here. The engine needs fuel when it needs it, not later.
When looking over the internal parts, do this for the floats as well. When they are in your hand, shake them. Listen for sloshing fuel. If you hear or feel any of that, replace the offending float. Note and as hinted, for some crazy reason, there are two types of floats for these carbs so snag the style you have.
Between us? Having spent some years using electronic fuel injection, I smilingly call a carburetor a “controlled leak”. Carbs are dead simple and in a pinch, I prefer them as it is hard to get one to fail but boy howdy can they be ornery to tune at times. Don’t forget that Honda and Keihin have done the heavy lifting here so all we need to do is to put things, like float levels, back where they belong all nice and clean like.
After the carbs were on the bike, I fed some fuel to it and the bike fired up almost instantly. BTW, hanging a small fuel container nearby gives you far greater access to the carbs just in case. You know, in case its best to remove them again. The CB’s fuel tank hides a lot even though you can still work and tune with the OE tank in place. As you may recall, we set the carb slide as low as they’d go so when you fire the engine, you will have to hold the throttle up a bit whilst allowing time for the engine to warm. A warm engine prefers a slightly different “tune” than a cold one so don’t rush it. Last I checked, the engines are nice and warm when we ride them right?
Back to the basics:
1) check, and set if needed, valve clearance.
2) check, and set if necessary, the ignition timing. Once those are known and you are happy, proceed with the carb!
4) Now with the carbs bolted onto the engine, with good O rings on carb and manifold, verify your needle position one more time is there is any concern. So long as they are the same, proceed. In my case, I have my 22402 needles at second richest setting.
As can be seen here, my clip is in the slot position of the red arrow which raises the needles up in the slide to the second highest slot. In my case, I might even try the needle as high as it will go (last slot to the right of the arrow) but I’m getting ahead of myself. Needle height is a quick and easy change.
Once both slides are in, now it is time to mess with the throttle cables and how the slides respond to the twist of your wrist. (And yes, Keith Code’s books called A Twist of the Wrist are well worth the read) The goal here is to have both slides lift together. This is easy to do using your hand to touch the slides as you gently twist the throttle grip.
To get both slides to raise together, simply go to the adjuster on the carb that is not moving up when the other one does! Won’t take a lot, and before you know it, both slides move at the same time when opening the throttle.
The small screwdriver at the top of the pict is touching the adjuster. Raising the adjuster forces the carb slide to raise earlier because you've removed a bit of slack. Again, this rarely take a lot of adjustment.
Now the fun part. Once the engine is finally warm, turn in the idle speed screws (brass screw as seen above which looks like the cable luber is pointing to) until the engine is idling about where it ought to be. The manual says below 1000 rpm but me, I like a little more. Make sure you have raised the slides by their screws equally for this first swing at it until you can let go of the throttle and the engine will idle by itself.
Now you need to "balance" the carbs. That means that each cylinder is doing roughly the same work. There are tools to really get this close but you can come dang close yourself without the tools by feeling for equal exhaust pulsing or by the sound of using a 3/4” tube in your ear held at right angles to the carb throat. Like the feeling exhaust pulses, adjust carbs to provide the same sound from each carb. I swear, works well.
Tried to find the "stick" guy again to give him a shout out but of course....What Guy? Kudos to him.On the left, the commercially available Uni-Syn. Works well, super easy to use. Just place and hold it onto the front opening of the carb and watch the little red indicator move. The goal is to make the red indicator be at the same level of that vertical clear tube for each carb. Now on the right, this is something new to me which I found whilst looking around I saw this and LOVE its simplicity though I’ve never tried it. You use a couple of sticks stuck into each carb levered under the open leading edge of the slide. As you move the slide up or down, the sticks move up and down. When sticks are at the same level, you are golden. Again, I’ve never used it but love the idea. Between the tubes in my ears, tools like the Uni-Syn or sticks along with the ability to feel the exhaust pulsing, I’m covered. You will be too.
Once you have an acceptable idle all “synched up”, now mess with your idle mixture screws. Again, some brass looking screws seen in the GREEN circle. These are angled up slightly. The Red circle shows the engine speed adjuster.
This little baby in the green circle adjusts the air/fuel mixture at idle and can raise and lower the RPM. Most people suggest turning it in or out to find the highest RPM which I do at times but often once I've found that sweet spot, I then turn the screw back in 1/8th to 1/4 turn. (this is richer). This will most likely lose you a few rpm but often I find the gains of off idle response is a worth while trade. Unlike most cars and many motorcycles, there is no accelerator pump to help the carb/engine through this tough area of carburation. YMMV so give it a whirl and settle on what works best for you.
Once you are happy with the mixture, you will most likely want to go back and set the idle speed to what you want which is where you may have been initially. Make sure you adjust the idle speed screws equally but feel free to re-visit the synching thing if you feel you messed it up. Remember? Ear, Vacuum, Sticks, exhaust pulsing, all quick and simple to do.
Now, shut the engine down and with your hand, check that the slides still move together. Very often you’ll find that this has changed because your idle speed screw is holding one slide higher than it did when we started. (Don't forget the slides were sitting on the floor of the carb body when we began) Changing the idles screws typically raises one slide higher than the next putting cable slack into that side. So like before, just take the slack out again with the adjuster on top of the carb. This can be a bit of a tap dance but no matter what, it is all very easy.
OK, I'm toast for now so....Later!
PS, if someone has a nice float bowl no longer wanted....feel free to reach out. I'm trusting the Epoxy but there's always a but... TY
Last edited:
Hans Freekit
Well-known Member
Awesome description. Kudos.
Pridanc
Veteran Member
#32 addendum
First off, sorry to have gone silent but as I age, so do those around me and we've needed to help family. My apologies
So, after all my blathering above about carbs, I did order some larger pilot jets. I have gone from a #35 to a 38. I just didn't like the initial throttle response right off idle which we all know can be affected by a myriad of things (remember: Carb=controlled leak) but at this juncture I knew that this wasn't so large as to stop me from adjusting around it with the idle mixture screw. With the 35's the idle mixture screw was maybe 1/8th turn out from bottomed.
As I didn't have the correct short stubby screwdriver with the correct blade to safely grab the pilot jets with the carbs still on the engine, I pulled the carbs and got 'er done. However after putting the carbs back onto the engine, followed by the slides back into the bodies, I casually checked the slides lifting equally as they were prior to this recent removal. Wow, good thing I did as I once again tripped over what was now an issue. Even though I'd had this issue before, I did not recognize it as one. Humbug.
Long story...even longer...the left carb was now clearly hanging up. To be more accurate, its slide was again way behind the right carb's slide. On the surface we can easily take the slack up with the carb/cable adjuster and I did. But this always left the slide raised off its Idle Screw (not good) even if the slide now rose with the other. WT absolute heck was going on? How is that even possible. As mentioned, this had happened before but whilst messing with the carbs/cables the issue cleared itself unbeknownst to me so I thought I was golden. Again, I'd no idea there was even a potential issue until pulling the carbs for the jet change. Not happy that this was now an issue, but happy that I did as I now realized I had an issue and must address it. Dodged a bullet here I think.
So lets now discuss how I addressed it and along the way, please remember I've never seen or touched an old CB before so as I dismantled it, I did my best to copy or emulate what was. This, to me, might be one of those times when what I found was never right. Again, say I, the expert.
Completely flummoxed, it was time to start with the absolute basics. Pull the carbs off, along with the entire throttle-cable system. Dismantle and start measuring every part.
As this picture of a throttle cable control system is a good one, I felt I'd use it even if it is not from this CB72 but from an old BMW. It is great for our purposes here. The Honda "parts picture" of this is sketchy at best.
In my case, the cap of the splitter seen here #16, and the body #14, are swapped around. That is, the cap #16 of the splitter on this Honda receives the single cable #12 from the throttle itself and the lower part of the body has the two carb cable housing receivers. Now, drum roll, the "shuttle" #15 is way different on this Honda. For reference, this bike came with an aluminum splitter which is what I kept. Back to the "if it can be salvaged or reused", I will do that.
My concern here is that the Honda's #15 is a 5mm thick disc (fat washer) seen below that fits very loosely in the housing #14. Even if we can say this is unlikely, the disc can **** which can't be OK by any measure.
Now take a look at the #15 of the BMW which is significantly longer leaving it impossible to **** in the splitter tube. Because of this I drew up and then printed a copy of the BMW part to fit the Honda's aluminum splitter. Is this new part "better", I'm not sure here, but can it help add one more layer of accuracy whilst removing the chance of a tilt? It sure can, and so far it works a charm! Here are some drawings of it.
The original Honda "disc" measured 5.2mm long with a diameter of 10.4mm. The new part's overall length is now 13mm and the diameter is now 11.1mm. The new shuttle is not tight but the good news is that the plastic has almost zero expansion with heat where as the aluminum tube will expand without question. Plastics slide on aluminum all by their lonesome but if I need to apply some lubricant (unlikely), this plastic is good with that.
The long thin slot in the new part is to allow the single pull cable from the throttle grip to be slid into place without having to remove that cable's end (de-solder), then slide this over the cable along with a re-soldering of the cable end. You can see this in the picture of the original disc. To get the disc off of the cable will need removal of the cables end. Although I may end up doing the de-solder/re-solder trick, I'd only do so to eliminate the slot but so far this new "pull" (shuttle?) seems robust enough. I'll beat on it for a while before I make my final choice. The other two slots are for the carb cables and are there in the original "disc" too. I've also added troughs (wells?) for each cable head to reside in with the intent of removing any chance of the cables escape!
Bolting it all back together, right off the bat the carbs fell into line with dead simple adjustment. All that aside, I will dismantle them a few times to see if I can't recreate that previous issue hoping to clarify that it has truly been resolved.
And last few words on this. My brain is going "so if the thin, sloppy fit disc" was there when you dismantled it, how'd it work before? And do I know for a fact that the splitter was 100% as made and used from 1961? Clearly a no for both questions as I've no way to know that.
Regardless, so far so good and off to a) either the next posting here or b) to help a family member get settled. More to come.
First off, sorry to have gone silent but as I age, so do those around me and we've needed to help family. My apologies
So, after all my blathering above about carbs, I did order some larger pilot jets. I have gone from a #35 to a 38. I just didn't like the initial throttle response right off idle which we all know can be affected by a myriad of things (remember: Carb=controlled leak
) but at this juncture I knew that this wasn't so large as to stop me from adjusting around it with the idle mixture screw. With the 35's the idle mixture screw was maybe 1/8th turn out from bottomed.As I didn't have the correct short stubby screwdriver with the correct blade to safely grab the pilot jets with the carbs still on the engine, I pulled the carbs and got 'er done. However after putting the carbs back onto the engine, followed by the slides back into the bodies, I casually checked the slides lifting equally as they were prior to this recent removal. Wow, good thing I did as I once again tripped over what was now an issue. Even though I'd had this issue before, I did not recognize it as one. Humbug.
Long story...even longer...the left carb was now clearly hanging up. To be more accurate, its slide was again way behind the right carb's slide. On the surface we can easily take the slack up with the carb/cable adjuster and I did. But this always left the slide raised off its Idle Screw (not good) even if the slide now rose with the other. WT absolute heck was going on? How is that even possible. As mentioned, this had happened before but whilst messing with the carbs/cables the issue cleared itself unbeknownst to me so I thought I was golden. Again, I'd no idea there was even a potential issue until pulling the carbs for the jet change. Not happy that this was now an issue, but happy that I did as I now realized I had an issue and must address it. Dodged a bullet here I think.
So lets now discuss how I addressed it and along the way, please remember I've never seen or touched an old CB before so as I dismantled it, I did my best to copy or emulate what was. This, to me, might be one of those times when what I found was never right. Again, say I, the expert.
Completely flummoxed, it was time to start with the absolute basics. Pull the carbs off, along with the entire throttle-cable system. Dismantle and start measuring every part.
- Measured the carb cables. Both cables were exactly the same length. The cable housings were a different length by 1.22mm
- As I had looked at them before, not real sure why I didn't take notice but could be I'm OK here for the simple reason the carb caps have adjusters to make up for this difference.
- Now I measured the depth of each carb-slides cable retention hole. That is where there nub on the end of the throttle cable resides in the slide. With machining being the way it is, I couldn't imagine there would be a discrepancy much less one too large to correct with the adjusters on the carb caps. BTW, they were the same depth.
- Put the slides back into the carb bodies fully assembled with cables, screwed the caps back on to compare both cables at rest. This would indicate that the carb bodies were close to the same height which would leave the same amount of cable sticking out of its respective cable housing. Again, they were so close as to say there were identical other than the 1.22mm shorter housing mentioned above of one cable housing. This was easily dealt with using the adjuster.
As this picture of a throttle cable control system is a good one, I felt I'd use it even if it is not from this CB72 but from an old BMW. It is great for our purposes here. The Honda "parts picture" of this is sketchy at best.
In my case, the cap of the splitter seen here #16, and the body #14, are swapped around. That is, the cap #16 of the splitter on this Honda receives the single cable #12 from the throttle itself and the lower part of the body has the two carb cable housing receivers. Now, drum roll, the "shuttle" #15 is way different on this Honda. For reference, this bike came with an aluminum splitter which is what I kept. Back to the "if it can be salvaged or reused", I will do that.
My concern here is that the Honda's #15 is a 5mm thick disc (fat washer) seen below that fits very loosely in the housing #14. Even if we can say this is unlikely, the disc can **** which can't be OK by any measure.
Now take a look at the #15 of the BMW which is significantly longer leaving it impossible to **** in the splitter tube. Because of this I drew up and then printed a copy of the BMW part to fit the Honda's aluminum splitter. Is this new part "better", I'm not sure here, but can it help add one more layer of accuracy whilst removing the chance of a tilt? It sure can, and so far it works a charm! Here are some drawings of it.
The original Honda "disc" measured 5.2mm long with a diameter of 10.4mm. The new part's overall length is now 13mm and the diameter is now 11.1mm. The new shuttle is not tight but the good news is that the plastic has almost zero expansion with heat where as the aluminum tube will expand without question. Plastics slide on aluminum all by their lonesome but if I need to apply some lubricant (unlikely), this plastic is good with that.
The long thin slot in the new part is to allow the single pull cable from the throttle grip to be slid into place without having to remove that cable's end (de-solder), then slide this over the cable along with a re-soldering of the cable end. You can see this in the picture of the original disc. To get the disc off of the cable will need removal of the cables end. Although I may end up doing the de-solder/re-solder trick, I'd only do so to eliminate the slot but so far this new "pull" (shuttle?) seems robust enough. I'll beat on it for a while before I make my final choice. The other two slots are for the carb cables and are there in the original "disc" too. I've also added troughs (wells?) for each cable head to reside in with the intent of removing any chance of the cables escape!
Bolting it all back together, right off the bat the carbs fell into line with dead simple adjustment. All that aside, I will dismantle them a few times to see if I can't recreate that previous issue hoping to clarify that it has truly been resolved.
And last few words on this. My brain is going "so if the thin, sloppy fit disc" was there when you dismantled it, how'd it work before? And do I know for a fact that the splitter was 100% as made and used from 1961? Clearly a no for both questions as I've no way to know that.
Regardless, so far so good and off to a) either the next posting here or b) to help a family member get settled. More to come.
Last edited: