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    AD

A Bomber barn find

Here's A trick I picked up way back when. It may be just be the ticket with your hearing. Take an old matchbook, the small ones with the flap(don't even know if these still exist), open it up and hold the flap against the outlet of the exhaust. Makes a very distinct sound that makes it easier to sync the carbs. Oh, maybe remove the matches.

Nice !, and if you hold your hands (open and stretched) +/- 1-2 inches from the exit, and close your eyes en concentrate on the pressure from the gas, you will be able to dial them in within a few minutes. You have to do this a few times, or you could practice with a (twin) bike with vacuum connections and a mercury gauges to get the hang of it....
 
This is what I have been doing, and the pressure is very different. We're in a run of very wet, drippy weather for the next few days so I won't be working on the bike with a running engine, but then I'm going to try fiddling with the idle speed on both carbs to see if I can get them in better balance.

I've had Hondas where the vacuum pistons were different left and right but everything I see shows these are not. I did once have a bike where the piston was backwards on each side and all it did was rev like crazy, and when I swapped them it was fine. These can't go in backwards, but I was wondering if I had a wrong piston in one carb - turns out left and right have the same part number.
 
If you end up needing a replacement, I may have one and, if so, you'd be welcome to it. I'm away from home at the moment and won't be able to check during the next two weeks.

I went through my spare parts and it seems that, foolishly, I did not keep the starter sprocket when I deleted the electric start on my 450. Sorry!
 
Fiddle the air/mixture screws and stationary screws for a while, these carburettors are very sensitive to the air/ mixture screws setting. Check if both air screws are the same type, you won't be the first one to find out that you have two different types ...
 
Update time. After cleaning and smoothing the starter sprocket surface I also replaced the little caps that go between the springs and the rollers in the starter clutch, and now everything works.

With the engine running and warmed up some the left side was still running poorly with very little exhaust pressure, so I experimented by just opening the throttle on the left to see if I could get a better balance. The engine did run faster but the exhaust pressure was still much less than the right side, and what was really interesting was that the left muffler got much hotter than the right. After all that I think there's probably a badly worn exhaust cam lobe on the left side and the valve doesn't open soon enough and close late enough. The follower I replaced, so that's OK, and the compression has tested OK a couple of times. There's still puffing back through the carb, and that smells like exhaust.

So now the decision is - do I put the energy into rebuilding the top end of this K4 engine or do I put the whole bike into temporary storage and put my energy into creating a running Bomber engine from the parts I have and things I have to find, like a head, valves and cams and all. I don't have room to do both at the same time. I'm leaning toward the Bomber engine project, but I'm not sure.
 
I just skimmed through the thread to familiarize myself again. It seems odd that it isn't running well on the left despite the strong compression numbers. I suppose you could take a look at the exhaust cam with the motor in the frame, but I'd also want to go through the carbs another time or two before pulling the motor for top end work. Have you seen Bill Lane's setup instructions for the carbs? Would be worth a read if not.

Since you have a black bomber and two partial k0 motors I can understand an interest in using one of those, but it seems like this motor is closer to being a runner than the others, even if you do the top end work.
 
I just skimmed through the thread to familiarize myself again. It seems odd that it isn't running well on the left despite the strong compression numbers. I suppose you could take a look at the exhaust cam with the motor in the frame, but I'd also want to go through the carbs another time or two before pulling the motor for top end work. Have you seen Bill Lane's setup instructions for the carbs? Would be worth a read if not.

Since you have a black bomber and two partial k0 motors I can understand an interest in using one of those, but it seems like this motor is closer to being a runner than the others, even if you do the top end work.

I appreciate your fast response. Just to fill in, I have taken the carbs apart several times, cleaned things thoroughly and put the carb bodies into a ultrasound bath of Pine-Sol and water. After that I blew carb cleaner through the passages, poked the tiny holes in the carb body at the throttle plate with a guitar string, opened the big screw on the bottom side of the idle air-fuel mix passage and blasted carb cleaner through and done what the set-up instructions suggest. I have done that on both carbs, and on a second set of carbs as well. The floats are set at 20, I have the gauge to do that. The rubber mounts have been replaced. I put a drop or two of 80-90 gear oil at each end of the throttle shafts. I gently cleaned the inside surfaces of the caps over the vacuum cylinders, and the cylinders themselves.

The mufflers are after market straight through. I can look through them from one end to the other, and they are clear.

I could try to measure the exhaust cam lobe in the engine. What would be the largest diameter of the cam lobe be?

The camshafts are timed correctly. The ignition is timed correctly. The coils and condensers were swapped to see if there was a variation, but there was not.

My thought about using the K0 lower was based on the thought that if the K4 head would be OK on the K0 lower why not create that sort of hybrid?
 
My thought about using the K0 lower was based on the thought that if the K4 head would be OK on the K0 lower why not create that sort of hybrid?

And it would be, I'm eventually going to be doing the same thing for my drag bike project, 5 speed head on a 4 speed bottom end.

Did you happen to check the header pipes in case the double wall in the left side had rusted and possibly collapsed a bit causing some additional restriction? It doesn't happen often, but has in some cases.
 
The carbs are clean but maybe not adjusted right or balanced right.

I was mainly wondering how things had gone when you synched and balanced the carbs. Bill Lane's instructions give a little more detail on that than what I've seen elsewhere. When I feel a difference in the exhaust pressure, I will back off the idle adjuster screw on the strong side a smidge and turn the weak one in. Then I go back to adjusting the mixture screws to find the max rpm. Does your left carb respond to changes in the mixture setting? And have you checked for air leaks? Recently, I had an issue where my left carb wasn't responding to mixture adjustments and, in fact, wasn't firing at idle. I ended up swapping out the throttle plate and the problem went away. Did you have your throttle plates out at any point?

I could try to measure the exhaust cam lobe in the engine. What would be the largest diameter of the cam lobe be?

Maybe AD can answer this question. I see the lift spec in the FSM, but not the actual lobe diameter.

My thought about using the K0 lower was based on the thought that if the K4 head would be OK on the K0 lower why not create that sort of hybrid?

I wasn't aware that the later head could be used with the 4-speed bottom end, but that's good to know. I guess this head would need to be sorted out or replaced either way.

Did you happen to check the header pipes in case the double wall in the left side had rusted and possibly collapsed a bit causing some additional restriction? It doesn't happen often, but has in some cases.

I had wondered about the header as well, since it was only mentioned that the mufflers are clear. Seems unlikely that the header would be the problem, but it's easy to check.

I think AD recently had an ignition issue on one side that resulted from a bad condenser ground. Wouldn't hurt to check that either.
 
Maybe AD can answer this question. I see the lift spec in the FSM, but not the actual lobe diameter.

I think AD recently had an ignition issue on one side that resulted from a bad condenser ground. Wouldn't hurt to check that either.

I do not know the actual lobe diameter of the stock cam. My condenser issue was the connectors in the coil plugs, when I went to check them one had come loose (probably long-term vibration) and the other fell out as I was moving the wiring around to check. I simply squeezed the female connectors a bit and plugged them back in, so it wasn't the ground side. And, it didn't affect the idle (or a negligible effect if at all), the issue was on acceleration above about 2500 to 3000 rpm, it missed horribly.
 
Some good thoughts. I'll check the header. The throttle plate is easy enough to get to as well, but what am I looking for? Clearly it needs to be centered and snug. Should the tiny holes in the carb body at the base of the closed throttle plate be visible or hidden with the plate closed? All 3? Visible from the engine side.

Turning the idle adjust screw in on the weak side did help raise the rpms but the pressure coming out the exhaust was still far less on the left than the right. And the left muffler all the way to the tip got really hot, fast, while the right side remained cool far longer. After maybe 5 minutes at idle I couldn't touch the muffler tip on the left, but I could grab and hold the tip on the right.
 
Some good thoughts. I'll check the header. The throttle plate is easy enough to get to as well, but what am I looking for? Clearly it needs to be centered and snug. Should the tiny holes in the carb body at the base of the closed throttle plate be visible or hidden with the plate closed? All 3? Visible from the engine side.

Turning the idle adjust screw in on the weak side did help raise the rpms but the pressure coming out the exhaust was still far less on the left than the right. And the left muffler all the way to the tip got really hot, fast, while the right side remained cool far longer. After maybe 5 minutes at idle I couldn't touch the muffler tip on the left, but I could grab and hold the tip on the right.

The throttle plates have an orientation. The edges are beveled to allow the plate to seat properly in the venturi and if installed in the wrong orientation or slightly out of position by a previous owner they may not close all the way. This could allow more air to pass through on that carb. The beveled edge is on the bottom-front and top-back of the plate, to prevent binding as the plate closes. I have the later 723A carbs with only two holes and I think the plate will just about cover them when fully closed. I'm not sure if all three should be covered on the 14H carbs, but I suspect not the third. It would be good to look for any differences in the fully closed positions for the two carbs.

How does the right respond to the mixture screw? I would think you should be able to get it close to a stall by backing off the idle adjuster and gently seating the mixture screw. If not, it's still getting air/fuel mixture somehow. How far out are the mixture screws?

The hot pipe on the left is concerning. Turning in the mixture screw leans the mixture, which would make it run hotter. Are you able to measure the header temps? I don't know what they should be, but you wouldn't want to see a huge difference and it sounds like you are. The strangest thing is that the side with greater exhaust pressure is running colder.

I hope you find something that will lead to an improvement.
 
The 1st hole, closest to the engine, is the idle mixture port. Other holes are called transition ports that act to enrichen the mixture as the throttle plate opens giving a smooth transition from the idle circuit to the main.
So the 1st hole should be uncovered with the throttle closed but the other(s) hidden.
 
I took out the throttle plate from the left (slow, low exhaust pressure) carb. In the photos it was the one on the right with the Sharpee. What you can't see well is that the marking for the Keihin part number was up, upside down when viewed from the open end of the carb.

View attachment 12816Throttle plates engine side.jpg

The beveled rim was facing the correct way so the sides on the plate would set correctly against the body of the carb.

Here's the other side of the plates, old one now on the left.

View attachment 12817Throttle plates intake side.jpg

There is a slight bevel machined onto the back of the throttle plate which is supposed to be down, I think, to allow the idle jet outlet to bleed fuel in at closed throttle. I'm going to put in the replacement plate, on your left in the photo, because the old one was obviously messed up - the mounting screws carved into the side of the plate.
 
I hope the replacement will lead to an improvement. For the benefit of anyone reading this thread in the future, I thought I would make a crude picture of the proper bevel orientation. My understanding is that the bevel prevents the plate from binding as it closes, so it can close off air flow through the venturi. On the top of the plate, the beveled edge should be on the back side, whereas on the bottom of the plate it should be on the front/engine side.
throttleshaft.png
 
Inspect the edges of the bevels, any damage there means a new one is needed.
Damage is usually in the form of a dent on the edge, this allows air to flow past the throttle plate in a close position, idle, and can make it difficult to set the idle speed and mixture.
 
I've been cleaning carbs for years and never knew about these beveled edges. Ignorance has been bliss, until now. But now I can see exactly why they exist and I'll be careful to check. Thanks for your expertise @stl360+450 and @LongDistanceRider.
 
Well, as a last gasp effort before I take the engine out of the frame I took off the left side header pipe. Somethings in there, around the bend part way. I can push a plumbing snake in from the head end about 8 inches to a dead stop, CLUNK. From the exhaust I can push the snake in almost to the same point. I deliberately dropped a large nut into the head end and it went in and stopped. I could dump it out, no problem. Nothing rattles. I held the exhaust end in my hand and banged the head end down on a wood block - nothing. Tried a long, flexible grabber thing I have, nothing to grab that I could feel. I don't have a scope. What next?

I could bang my head against it.
 
Wow. That sounds really strange, but makes sense given everything else. You couldn't get the nut to pass through the restricted section? I'd go for a replacement header. Maybe the double wall collapsed as AD suggested could be the case.

You might try bending a metal coat hanger to the right shape to try feeling the blocked area a little better, but unless there's something jammed in there, I think a replacement is in order.
 
Sounds like the double wall collapsed, there's no cure really unless you can get something to go around the curve and still allow you to apply lots of force to break thru.
 
I tried running a good blast of water through. More can back at me than went through, but some did, which is exactly what the output felt like at the end of the muffler. So, something large is in there. I'm going to snoop around and see if anyone I know has an endoscope.
 
The interior wall definitely bulged out and closed off almost the entire exhaust pipe. I was able to see a bit of it with a mirror on a stick and a good headlight. I wet the inside and the reflections showed a bulge where there should be the inside of a tube. No sign of anything on the outside. With a big screwdriver and a 4 pound sledge I could pound some of it down, not all for sure, and the rest is too far around the curve. I put the pipe back on and the engine runs much better, not great but better.

A replacement pipe is the solution. Way better than a complete top end overhaul.
 
That should certainly explain the heat on that side, so this seems to be good news. I'm looking forward to the next update with the replacement header.

I decided to order one of those Android boroscopes ($12 variety) to see how well it works. I have an old exhaust from my XL350 that seemed to be restricted and made the bike run hot, maybe I'll have a look see inside...
 
The interior wall definitely bulged out and closed off almost the entire exhaust pipe.

It was a shot in the dark when I mentioned it, but I have seen it before a few times and not all that recently either so it can take far less years to happen than yours might have. It's funny how some things are just a given until it ends up being the last thing you look at, and it turns out to be the culprit.
 
I'm really glad you mentioned it. What a relief! And I never even considered that the pipe might be two layers. The outside looks fine so I just assumed (there it is again, making assumptions that turn out to be completely wrong) it was OK.
 
I'm really glad you mentioned it. What a relief! And I never even considered that the pipe might be two layers. The outside looks fine so I just assumed (there it is again, making assumptions that turn out to be completely wrong) it was OK.

That's one of those old memories from when I first started working on these bikes, learning that Honda did the double wall pipes to help keep them from turning yellow from the heat. They knew how much combustion temperature their high performance engines were putting out and likely paid attention to how the Harleys and Brit bikes pipes all turned yellow.
 
I think Honda used double wall pipes not for pipe discoloration but to keep the exhaust gasses hotter for longer which makes them flow faster helping with scavenging the combustion chamber. Performance increase.
 
While working at the dealerships it was said that the purpose was for discoloration, but you're probably right when I think back to some of the guys I worked with... you wouldn't mistake them for Honda engineers, for sure
 
I have double wall headers, and after fast highway rides with speeds around 80 mls/hr (highway speed limit) for longer periods, the headers will discolour into a blue-yellow pattern. This picture is taken just before getting home after a 2.5 hours ride @ 80 mls/hr, covering a distance of 230 km, one petrol stop only. No lean mixture according to the gas analyser of the yearly dyno run.

PA100002.jpg
 
While working at the dealerships it was said that the purpose was for discoloration . . .

Now THIS is interesting, along with the points raised by LDR and Jensen.

I was also told during my Honda mechanic time that the double pipe was to prevent discolouration. I had never heard about the 'hotter flowing gases' theory (but do not argue against it). We were always told that blueing pipes is a result of incorrect carburation, i.e. too lean. I wonder if the late, learned Soichiro Honda didn't want his exhausts to look like those of the British bikes of the day?

Now, some 50-odd years on, the boy racers strive to get blue on their titanium headers.:rolleyes:
 
If you measure the inner pipe diameter you'll find it closely matches the exhaust port. This is all in done to keep the exhaust gasses flowing hot and fast. A little not so light reading on this theory can be found in Scientific Design of Intake and Exhaust System written in the 60's and still used in engineering schools.
 
Over the years I've gained a lot of respect for the Honda engineers, and for the Honda company that gives them what looks like a lot of power to influence their products. The double wall pipes are there for a reason, and this problem is rare from all I can find out. And it's sure a lot easier to replace them than to replace a cam chain idler or a transmission bushing.
 
Over the years I've gained a lot of respect for the Honda engineers, and for the Honda company that gives them what looks like a lot of power to influence their products. The double wall pipes are there for a reason, and this problem is rare from all I can find out. And it's sure a lot easier to replace them than to replace a cam chain idler or a transmission bushing.

I've always admired what the Honda engineers did during the era of slide rules and legal pads. They basically taught the world that getting more horsepower out of an engine can be done in ways no one dreamed of prior to their road racing efforts and research, and that reliability doesn't have to be compromised to get it. If it weren't for Honda, you wonder how long the industry would have been with pushrod, long stroke engines
 
Keeping the exhaust gases hotter is one of the advertised benefits of Cerakote, both on the inside and outside of pipes.

Also the original reason for exhaust wrapping, before the owners of rat bikes adopted it, using this as an excuse to cover up their rusted header pipes.

Most after market header pipes, for example the CB175/200 ones from DS, are single skinned. With the same OD as the genuine pipes, they have a larger ID, which must also have some effect on performance. They also blue more readily.

EDIT I've sawn up an original CB600 system and the (stainless steel) header pipes on that are single skinned. Cheaper to make, I suppose.
 
. . . Most after market header pipes, for example the CB175/200 ones from DS, are single skinned. . . They also blue more readily. . .

Good info as I currently have headers and full exhausts on order from DS.

No way do I want blue pipes, so I won't exceed 3,000 rpm and ride only in winter.:sad:
 
I suppose there's some insulating effect of a laminated pipe, and maybe there's some industrial reason for or against lamination when bending pipes. The effect of friction on the exhaust is in that book about intake and exhaust technology (from 1972) but there's really no discussion about the friction differences of different pipe materials. 50 years later there probably is much more information, most of it written in language that uses words and concepts I don't really understand. Now it seems like there are two completely different sets of values about pipes. Street and cruiser bikes put a lot of emphasis on style, sport bikes are focused on weight distribution. And both have to comply with emissions rules, too.

These vintage Honda Twins do have a lot of sophisticated design buried in what looks primitive today.
 
These vintage Honda Twins do have a lot of sophisticated design buried in what looks primitive today.

That's one of the things to be admired so much, the fact that they thought of many advanced ideas and incorporated them into the bikes then without a lot of hoopla or crazy physical (visual) manifestation of it while keeping the styling fairly fresh for the era. Just another reason they're still around after so many decades.
 
Me, too. I'm quietly sitting here waiting. The last update said the box left the San Francisco network distribution center at 3:38 am 2/21/2022. Probably on the way to Fresno, so it can be rerouted to Oakland, via Redding. Or, since today is a holiday, maybe it'll serve as a dining table for somebody having their lunch.
 
The latest info from our Postal Service is that the box should arrive by 9 pm tomorrow, the 22nd. BRING IT ON!
 
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