1972 CB450 K5 Hot Mess

RobMan said:
I also wonder if the gas cap is venting properly, it is new one that i bought off Amazon and looks nice but may not be venting properly so I will do the next run with the cap loose.
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Some of the aftermarket gas caps have wadding material inside that may restrict airflow. On my CB350 build, I bought a black gas cap from 4-into-1 and removed the wadding before installation. Can yours be taken apart like the one shown below? If so, you might check for wadding.

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Someone had purchased the same style cap before me and I benefited from them having a venting issue and posting about it.
 
stl360+450 said:
Some of the aftermarket gas caps have wadding material inside that may restrict airflow. On my CB350 build, I bought a black gas cap from 4-into-1 and removed the wadding before installation. Can yours be taken apart like the one shown below? If so, you might check for wadding.

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Someone had purchased the same style cap before me and I benefited from them having a venting issue and posting about it.
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Thanks for the tip! Yes mine looks just like that and I will take it apart and check for wadding. They do advertise it as being less likely to leak than the original and that is probably what the wadding is for.
 
Too cold to do much but I was curious so took the fuel cap guts apart and removed the wadding, a small plug about the size of an aspirin. It must have been positioned right between the two small vent holes in the plates and is pretty dense so I can see where it would restrict air flow. It is supposed to be warmer on Thursday so perhaps another test run to see if it makes any difference.

Picture of the guts.

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Pretty nice today around 50 degrees so decided to do a test run and see if removing the wadding from the fuel cap vent made any difference and the answer is no. Start it, let it warm up and running pretty good, idle still needs to be fine tuned but shouldn't make a difference in mid range and high speed running. take off and runs great out the gate 1st-4th, 4 to 5 K shift points then bog city. Seems like one cylinder just shutting off. Turn around and limp home and not really finding any issues on the post flight. Check spark both sides good, spark plugs not fouled, compression check, warm engine about 165 both cylinders which is a little low but my tester, which has a rubber hose and is pretty old, may be off a bit.

It is pretty consistent on about how far I get before it starts running poorly so my next thought is back to am I running out of fuel, so is the petcock plugged or problematic and I am running out of gas. The petcock is a re-pop from David Silver so hopefully a good quality one but who knows, I do have an original that probably needs a kit that I might try. I see 4into1 has the kit for $17.95 and includes a new screen and wondering if anyone has experience with them?

Appreciate any thoughts and suggestions at this point. Thanks.
 
stl360+450 said:
If you're able to safely pull over when this happens, I would shut off the petcock, pull over, and check the fuel level in each bowl. It would be nice to narrow the problem down.
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Yes that is a good idea, pull over and shut petcock and bike off immediately and then pull the bowls and see what the levels look like. It seems like it is running out of gas but heck who know, bad condenser or coil failing when stressed a bit. I will find it, just don't want to throw money at at the problem.
 
How is the charging system? Did you ever look at the voltage across the battery terminals while the motor is running?

I assume you're using electric start, which would quickly show signs of poor charging, unless you also have the battery on a tender between test runs.
 
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If I remember I did check the charging system early on after getting it running and I got about 14 volts when I would run the engine up a bit so believe it is charging OK but I do need to take another look. I have been charging the battery between test runs and I don't think low battery is part of the problem but I am not ruling anything out. It is such a “The thrill of victory and the agony of defeat“ all in about 10 seconds from pulling out on the road until it bogs down! The good thing is I believe it is mechanically sound but I just got to chase down this ghost. I may need to check the valve clearances again to make sure I don't have them too tight and valves not fully closing when it gets hot. Yep chasing ghosts.
 
Beautiful day here in North Carolina so finally got some time in the garage. As a reminder I am trying to sort out why the bike will take off fine but by the time I hit 4th it starts bogging down and feels like only hitting on one cylinder. Felt like fuel starvation or a bad condenser or coil. A prime suspect was the aftermarket petcock. I checked to see if it there was any crud in the screen and tested to see if it was flowing OK. I saw that fuel only flowed from one tap until it capped and then would flow from the other. I had rebuilt the OEM petcock the other day so swapped it out and fuel flowed from both taps evenly. Hummmm!

Bench checked the condensers and coils and the tested good with an ohm meter. Also checked the caps again just for giggles and found one open. The brass plug had vibrated loose and I had to tighten it up and then it tested good. I think a tiny drop of threadlock is in order. You can see a pic of one disassembled post #1285.

Put the tank back on and started it up which took several tries even though it was warm today. After starting it was seemed to be running OK but I noted there was a big difference between the exhaust pressure out of the mufflers with the right side very weak even when I blipped the right carb. Both header pipes getting hot but I could hear a bit of ratting from the right muffler so I decided to remove the mufflers to see how it would run with just open headers. I wish I had taken a video so you could hear the sound on the right, I can't really describe it but it was an oh crap sound, kinda like chocking a goose or something. Checked the exhaust pressure and very noticeable difference. Remembering that the exhaust headers for these bikes are double walled I took my long flexible mechanical fingers and ran it up the right header and it stopped right at the bend. Checked the left and it was open to the head. Pulled the right header and tried from the head side and it was blocked.

I believe the inner wall of the header started failing on my initial test drive and got progressively worse until it is almost completely blocked at this point. I was planning to replace the headers and mufflers at some point but just due to cosmetics. Plans change. :sneaky: I just started looking for new headers and saw DSS has them for about $260 and it looks like everyone else is quite proud of them even for used ones. Looking on the bright side it it was going to fail I am glad it did it at this point and not 20 or 30 miles from home.

That's my story and I'm sticking to it.
 
Emailed DSS to see if the headers they sell are double or single wall and if they are chrome or stainless steel. They say a "A high quality pair of reproduction down pipes" but I would be surprised if double walled.
 
Geez, man. That’s a weird one. Crazy spot to get enough moisture to cause that kind of corrosion - would have been the absolute last place I would have looked.
 
I am not sure it is due to corrosion, I used my cheap bore scope and I couldn't see any broke metal or corroded holes, I really couldn't see that well but more like the inner wall bubbled out. Possibly moisture was trapped in between the inner walls and turned to steam when heated and separated the inner wall. It is similar to a problem I had in the Air Force on a F4 Phantom where a large fuel transfer hose de-laminated on the inside and a flap of rubber acted like a one way check valve. Gave me fits until an old (to me at the time) Master Sargent told me what to look for. :)
 
Any chance you can remedy the collapsed wall using brute force? (hammer and some sort of steel rod) Then you could do a little more riding while you wait for the replacements.
 
stl360+450 said:
Any chance you can remedy the collapsed wall using brute force? (hammer and some sort of steel rod) Then you could do a little more riding while you wait for the replacements.
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Possibly and I may give it a shot. I was thinking of cutting it right at the bad section just to see what had happened. I could always practice my welding skills or lack of after taking a look.
 
Got a reply from Matt at DSS this morning and the down pipes they sell are single wall and chromed. Looked around a bit on line and all the used ones are, well used and the only new ones are from Thailand and once you include shipping and tariff I decided to bite the bullet and placed the order this morning with DSS. Also ordered new header to muffler clamps and a couple other small items. All the items are coming from across the pond so will be a couple of weeks. Patience weed hopper patience, when you can take the bolt from my hand you will be ready. BTW the cost doesn't bother me at all.

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RobMan said:
Got a reply from Matt at DSS this morning and the down pipes they sell are single wall and chromed. Looked around a bit on line and all the used ones are, well used and the only new ones are from Thailand and once you include shipping and tariff I decided to bite the bullet and placed the order this morning with DSS. Also ordered new header to muffler clamps and a couple other small items. All the items are coming from across the pond so will be a couple of weeks. Patience weed hopper patience, when you can take the bolt from my hand you will be ready. BTW the cost doesn't bother me at all.

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Hell. I was going to drop the link for the Delkevic 2-1 they have for the K3-K7…
 
It was my Bomber that had the collapsed inner tube on the header. I tried to hit it with a long tire iron and a 4 pound sledge hammer, but no luck. The curve makes it mostly inaccessible with a straight piece of steel. Just to prove the theory, I ran water from the hose tap into the engine end of the header, and it just overflowed, quickly. Replacement did the job, instant satisfaction.

Here's a link to my thread from February, 2022, where my post sounds just like yours.

"A Bomber Barn find", page 2
 
wentwest said:
It was my Bomber that had the collapsed inner tube on the header. I tried to hit it with a long tire iron and a 4 pound sledge hammer, but no luck. The curve makes it mostly inaccessible with a straight piece of steel. Just to prove the theory, I ran water from the hose tap into the engine end of the header, and it just overflowed, quickly. Replacement did the job, instant satisfaction.

Here's a link to my thread from February, 2022, where my post sounds just like yours.

"A Bomber Barn find", page 2
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Thanks Bob, I couldn't remember if it was Troy's or yours or whose it was.
 
EzPete said:
I was going to drop the link for the Delkevic 2-1 they have for the K3-K7…
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I was almost going to suggest considering aftermarket options like that. I like the look of the 2-1's as long as there is no kicker interference. They do complicate carb balancing on these bikes.
 
For inquiring minds I did cut the header at about where the obstruction started.

You can se how badly it is bulged in here. Also note there is actually 3 layers of pipe with the innermost coming down about 6 inches. The middle layer goes down until about 6 inches from the end of the pipe. I believe my theory of water trapped between the two outer layers is correct as you can see a small gap in the second photo, looking up muffler end, where moisture slowly infiltrated over the years and when pipe started heating up the layers sealed and steam does what steam does.


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RobMan said:
For inquiring minds I did cut the header at about where the obstruction started.

You can se how badly it is bulged in here. Also note there is actually 3 layers of pipe with the innermost coming down about 6 inches. The middle layer goes down until about 6 inches from the end of the pipe. I believe my theory of water trapped between the two outer layers is correct as you can see a small gap in the second photo, looking up muffler end, where moisture slowly infiltrated over the years and when pipe started heating up the layers sealed and steam does what steam does.


View attachment 54956View attachment 54957
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Wow that got really deformed.
 
spideypop said:
Nice find Rob! Hopefully the new headers will be the solution. BTW nice new picture. Funny I was looking for your old pic to see what's new on your thread. Took me a minute to realize the "new you" ;)
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Thanks, I hope it is the solution as well. Wish the headers had been available here in the US, hate have to twiddle my thumbs waiting for them. Tried seeing if I could get the inner pipe to knock or pull out so I could weld the header back together but no luck so far. I need the equivalent of a metal grinding rotorooter. BTW glad to hear I'm not the only one having a hard time finding my threads with the new pic! :LOL:
 
Still waiting on the new headers but been working on the bike for the last few days. Did a variation of @stl360+450 's brute force suggestion and ended up cutting the bad section out of the header and then brute forced the collapsed inner wall out. Welded the header back together (UGLY WELDS) and took for a test ride several days ago. Ran a bit better but still had the bogging issue after about a 1/4 mile. Drat! Messed around off and on and today finally pulled the carbs today. Having issues with one of the replacement floats, would occasionally leak from overflow and then when I tweaked it then it wouldn't open with the bowl on. I ended up using the old floats although I was worried about the age the appear to work great. Used the clear tube method and fills to about 2mm below the bowl seam. Took for another test ride for about 2 miles and seemed to rum great, still needs idle tuning but pulls strong in all gears, (kept RPM's below 5.5 K). Of course when I got home seemed like I could heart little to much valve noise from the exhaust cam and the cam chain was rattling so need to check adjustment on those. Perhaps tomorrow or the next day.




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I'm pretty impressed with the welding! Given all the brute force involved, it's amazing that you could still mount them up.

Sounds like forward progress with regards to the floats!

Addendum: the underside of that rear fender is clean enough to eat off of!
 
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stl360+450 said:
I'm pretty impressed with the welding! Given all the brute force involved, it's amazing that you could still mount them up.

Sounds like forward progress with regards to the floats!

Addendum: the underside of that rear fender is clean enough to eat off of!
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Harbor Freight to the rescue, used a cheap cut off tool to cut the pipe after making alignment marks. I had to be careful knocking the inner pipe out by crushing it a little at a time with big vice grips and a long punch helped.

My welder is the cheapest flux core they sell so not suitable for heavy duty stuff. I have to remind myself this welder works best by a series of spot welds rather than a continuous bead like the stick welders I learned on in high school way back in the before times.

I just hope the old floats don't have pin holes or cracks. I got the new ones from 4into1 and I think I must have bent it or something.

To confirm, with a caliper do you measure with or without the gasket?

Yeah I wish all the chrome looked as good as the rear fender but heck I would be scared to ride it! :eek:
 
That is what I would assume as well otherwise why put the notches there. I watched a number of videos and there really wasn't a consensus among them. I did use the clear tube method after swapping the floats and they both measured identical to my un-calibrated eyeball so I decided to leave well enough alone. I have an old carb that i may play with to see if I can see what was wrong with the new floats or if it was just me. :D
 
RobMan said:
I just hope the old floats don't have pin holes or cracks. I got the new ones from 4into1 and I think I must have bent it or something.

To confirm, with a caliper do you measure with or without the gasket?
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I check floats for leaks by boiling some water and submerging them. Any leak will immediately bubble.

Also, I measure float height from the notch as mentioned.
 
Set the valves and adjusted the cam chain today and did find a couple of the valves a little loose. I set them at a tight 1.5 thousandths and for the cam chain I wanted to measure how much slack it had so I stuck the short end of an Allen wrench in the hole in the tensioner and marked with a sharpie and after adjusting looks like took up about .5mm of slack. Did a quick test run of about 2 miles and when I got back both valves and cam chain sounded OK. Very pleased so far, accelerates nicely, returns to idle and shifts through all gears properly. I was getting a little popping out the right exhaust occasionally so I am going to put the air filters back on and see if I can tune it a little more. Still waiting for the new headers from DSS.
 
Feeling a bit like Christmas, got the new header pipes and clamps today. Super well packaged and arrive in perfect condition. So Shiny!!! Made in Thailand and feel like solid heavy materials. Only visible difference is not marked with an L and R which could be a problem for dumb old country boy. I had also ordered a new rear axle nut to replace the rounded one that had seen too many bouts with a loose crescent wrench.

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Of course the real test is to mount them and check the fit. It has gotten colder again so not sure if I will make it to the garage today or not. Either way more to come.
 
RobMan said:
Only visible difference is not marked with an L and R which could be a problem for dumb old country boy.
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I'm guessing it will be more obvious when you (like would happen to me) pick the wrong one to put on the side you're starting on.... you know, the 50/50 choice that's always wrong the first try, or maybe you win this award

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RobMan said:
So Shiny!!! Made in Thailand and feel like solid heavy materials.
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They do look nice. Not to undercut DSS, but it makes me wonder if similar quality pipes are available any cheaper directly from the vendors in Thailand. I've found other exhaust parts that way through eBay for other bikes, like CB350 headers and a full exhaust for a friend's Yamaha XT250.

I'm anxiously awaiting warmer temperatures as well. Hope you can try these out soon.
 
stl360+450 said:
They do look nice. Not to undercut DSS, but it makes me wonder if similar quality pipes are available any cheaper directly from the vendors in Thailand. I've found other exhaust parts that way through eBay for other bikes, like CB350 headers and a full exhaust for a friend's Yamaha XT250.

I'm anxiously awaiting warmer temperatures as well. Hope you can try these out soon.
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I thought the same thing myself but I knew with DSS having a store front in the US there is no issue with tariffs and I didn't want to get in an issue with customs. I also like being able to reach out to DSS customer service if needed.
 
Warmed up enough I ventured into the garage and got the new headers and old mufflers installed. Took a bit of rubber hammer to persuade the right muffler to go on far enough. Installed the air filters and went for a start up and as usual a bit cold natured but after I got it started and warmed up a bit seemed to be running well. Too cold for my old bones to go for a ride but I am pretty confident she will behave herself at least for a short run. I will have to take it on progressively longer rides to build up confidence. I also need to add the Motorcycle coverage to our AAA account.

Short video of it idling, no Vrooom Vroom. :sneaky:

Idle 2-24-26.MOV

drive.google.com drive.google.com
 
RobMan said:
Warmed up enough I ventured into the garage and got the new headers and old mufflers installed. Took a bit of rubber hammer to persuade the right muffler to go on far enough. Installed the air filters and went for a start up and as usual a bit cold natured but after I got it started and warmed up a bit seemed to be running well. Too cold for my old bones to go for a ride but I am pretty confident she will behave herself at least for a short run. I will have to take it on progressively longer rides to build up confidence. I also need to add the Motorcycle coverage to our AAA account.

Short video of it idling, no Vrooom Vroom. :sneaky:

Idle 2-24-26.MOV

drive.google.com drive.google.com
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Sounds good, engine's pretty quiet inside and the idle sounds nice, steady and even.
 
Pulled the carbs back off the bike today so I could check the floats for any leaks. Checked the floats in some boiling water and one did have a leak where I had suspected seeing a crack. Drilled a small hole to drain any fuel but didn't appear to be any so soldered up with my Radio Shack soldering iron and electronic grade rosin core solder. Checked the float height both wet and dry and think I have both right. Put back together and too for a 8 mile ride and appeared to run perfect. The only issue was a rattle I believe is coming from the tachometer and when I got home it was stuck at 2K but engine sounded like normal idle. Stayed at 2K after shutting the engine down. Oh well that is the kind of problem I like if I have to have one. :p

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