Author Topic: 76 CB550 Cafe build (Read 86056 times)

wolf550 · « **Reply #625 on:** August 29, 2021, 06:48:00 PM »

usually when I forget to put my gas tank to the off position and leave it, my carbs will start to leak from the overflow also.
I read that before cutting off the engine most with cut off the fuel supply use the excess fuel from the lines leaving a little fuel in the carbs.

did your temporary fuel bag have a plug to stop fuel going to carbs?

tshrey · « **Reply #626 on:** August 29, 2021, 06:59:33 PM »

I have an on/off valve inline but I left it on. Isn't that the whole point of the floats? I don't ever turn off the petcock on my dirtbike unless I'm transporting it. Maybe this is just another thing I don't know about old bikes.

seanbarney41 · « **Reply #627 on:** August 29, 2021, 08:03:53 PM »

yeah these float valves often won't hold it back...especially with the greater head pressure of a remote tank. If the bike is not running, turn the petcock OFF ALWAYS!

And every time you disturb the carbs, the float/valve mechanism has to settle back into place and there is gonna be overflows until they do. It is a process. Pull the carbs and fiddle with the floats and you have to start that process all over again from the beginning.

desertrefugee · « **Reply #628 on:** August 30, 2021, 10:25:41 AM »

Quote from: tshrey on August 29, 2021, 06:59:33 PM

I have an on/off valve inline but I left it on. Isn't that the whole point of the floats? I don't ever turn off the petcock on my dirtbike unless I'm transporting it. Maybe this is just another thing I don't know about old bikes.

Look up hydrolock. View the carnage. Some are more prone than others - but early GLs (bent rods) and the CBX (holed case) can suffer catastrophic damage - just from leaving the petcock on.

tshrey · « **Reply #629 on:** September 02, 2021, 08:53:13 AM »

I understand hydrolock and the drain lines that prevent it if you have a problem with the floats not stopping the gas. I just didn't get that under normal operating conditions the floats don't actually stop the gas. Most of my road bikes have been fuel injected so that isn't an issue by all of my dirt bikes have had carbs and I never shut the gas off and never had a problem with it coming out of the overflow lines. I'll use the petcock to turn off the fuel whenever I shut off the bike going forward.

I got a latch set up under the seat and machined an aluminum post last night. Now just have to get the height of the post mount set correctly in the bodywork in order to use it.

tshrey · « **Reply #630 on:** September 05, 2021, 07:04:33 AM »

I have the stock carbs set up with what I think is a decent idle and then synchronized them. When I blip the throttle I get a nice immediate rpm punch but then it will hang at ~3k for a couple seconds before returning to idle. When I look up 'hanging idle' the answer is always that they are too lean, but if I go richer on the mixture screws the idle (once it is stable and back to normal) drops, which would indicate to mean that I don't want to be richer. Is it because I'm lean up in the higher rpms from the blip? I have 40 pilots and 115 mains right now.

tshrey · « **Reply #631 on:** September 09, 2021, 08:03:26 AM »

After talking to Mike at Jets R Us I have a new appreciation for the insanity of tuning a 50 year old motorcycle. Finding 'genuine keihin' jets is difficult to say the least and the number stamped on jets are numbers relative to a given series or vendor. I thought a #40 meant something universal; nope. Also, in my rebuild kit I noticed that the air mix screw holes are much larger than in the screws that came in the carbs (no reason to believe those are the 'right' ones either), so a turn on those two screws would result in hugely different amounts of extra air flow.

Not sure why I didn't just jump right to this, but after this conversation I'm done screwing around with guessing whether something is rich or lean and ordered a standalone AEM wideband gauge. For $150 I should have done this a year ago, I would be fully done tuning by now. Also managed to find an airbox on ebay that wasn't insanely priced - it says 1977 but I'm assuming the physical geometry didn't change between the carb changes from 76 to 77.

tshrey · « **Reply #632 on:** September 14, 2021, 05:42:13 AM »

Bung welded in, wiring is basically just power and ground. Sure enough, with the pilot jet marked 40 I'm in the 10 range on AFR even with the air screws turned out. I'll drop to the 38 today and retry.

Also got a stock airbox. Not enough room to slide it in place once the carbs are on, so I guess you put that in, install the carbs on the manifold boots and then wiggle the carb to airbox boots into place?

Shtonecb500 · « **Reply #633 on:** September 14, 2021, 06:28:23 AM »

Yes, you have to fit it in there and wiggle it all together, I use a heat gun and warm up everything and it makes life easier, some oil helps too if needed.

tshrey · « **Reply #634 on:** September 15, 2021, 06:53:11 AM »

Dropped down to the 38 pilot and same thing, even with 2.5 turns out on the air screw I'm at 10.5 AFR. Figuring I would be pulling the carbs again I shut off the gas to run off some of the fuel in the bowls and after a bit it dropped down to the 13-14 range. Going to have to rig something up with the drains to let me do the clear tube method, maybe something is just goofy with the floats in this carb set and they are running high.

joeyvans · « **Reply #635 on:** September 15, 2021, 02:33:18 PM »

Performing the clear tube method did wonders for my 550 stock carbs. The fuel levels were all over the board, even with the float heights all set to 22mm. I hope it works for you.

tshrey · « **Reply #636 on:** September 15, 2021, 02:41:53 PM »

That is great to hear. I'm really getting pretty frustrated and tired of pulling carbs off. Literally every other time I install them on the bike when I turn the gas on one of the overflows starts running. Gas off, tap a few times with a mallet and it stops. Everything is super clean inside, every time I pull them I pull the float needle and seat and look for any kind of sediment and see none. I put every float at 22mm on the nose but high bowl levels is the only thing that makes sense at this point.

goodtryer · « **Reply #637 on:** September 15, 2021, 05:10:56 PM »

Each time I read this thread, this article from Mike Nixon’s site come to mind: https://www.motorcycleproject.com/text/the_60-40_rule.html

Maybe it’s completely off base but I wonder if doing what he says could shed some light on your situation. On the plus side, it doesn’t cost anything and you don’t have to remove the carbs to try it.

Good luck!

tshrey · « **Reply #638 on:** September 15, 2021, 07:11:16 PM »

That is a good place to start. One thing that I have is data that most don't when doing this - my mixture is very rich. I don't have to guess, I have a meter. There is no indication that one of the spark plugs are bad, all four header pipes are within 2 degrees of each other when idling (and reading about 240 degrees at the first bend after a couple minutes). So somehow there is too much fuel in the mix even after dropping to a stock pilot on a larger engine with headwork. I rigged up a jig to test all this on the bench with the clear tubes and will be doing it with distilled water so that if my clear tube leaks I don't get gas everywhere. I'll know more tomorrow, stay tuned.

tshrey · « **Reply #639 on:** September 16, 2021, 10:55:17 AM »

So clear tube method shows all my levels are equal and if anything, a little low (~5mm below top of bowl).

Only thing left is a curiosity on the pilot jet. The small one pictured below is what came in the carbs (purchased separately, so no idea of their history), the larger one is what is spec'd in the 4into1 rebuild kit. The #40 that I purchased is the same (larger) size. Looking at JetRUs that smaller one would be what they call a 3G. I'll try that next, if I'm still crazy rich I have no idea how to proceed.

tshrey · « **Reply #640 on:** September 16, 2021, 11:10:35 AM »

I'm answering my own questions. Those pilot jets are for a 350. If the PO used them who know what emulsion tubes and needles are in it. I'm going to switch everything out to the 4into1 rebuilt components, maybe the needles are wrong enough to let extra fuel from the main jet through.

tshrey · « **Reply #641 on:** September 20, 2021, 01:58:23 PM »

Pretty big day in the garage. Actual correct rebuild kit for 022A carbs installed and low and behold I have a nice, smooth 1100 rpm idle with an A/F ratio of 14:1. Revs very well and idle doesn't hang anymore. Also doesn't leak fuel out of the overflows. Time to get the new seat latch done so I can pop the seat on and off easily, mark the throttle tube for 1/4,1/2 and 3/4 and then ride it and check A/F throughout the throttle range. Drinking a beer in celebration.

MRieck · « **Reply #642 on:** September 20, 2021, 02:18:41 PM »

Quote from: tshrey on September 20, 2021, 01:58:23 PM

Pretty big day in the garage. Actual correct rebuild kit for 022A carbs installed and low and behold I have a nice, smooth 1100 rpm idle with an A/F ratio of 14:1. Revs very well and idle doesn't hang anymore. Also doesn't leak fuel out of the overflows. Time to get the new seat latch done so I can pop the seat on and off easily, mark the throttle tube for 1/4,1/2 and 3/4 and then ride it and check A/F throughout the throttle range. Drinking a beer in celebration.

Funny how that works brother.

Jimcg · « **Reply #643 on:** September 20, 2021, 11:01:17 PM »

Quote from: tshrey on September 20, 2021, 01:58:23 PM

Pretty big day in the garage. Actual correct rebuild kit for 022A carbs installed and low and behold I have a nice, smooth 1100 rpm idle with an A/F ratio of 14:1. Revs very well and idle doesn't hang anymore. Also doesn't leak fuel out of the overflows. Time to get the new seat latch done so I can pop the seat on and off easily, mark the throttle tube for 1/4,1/2 and 3/4 and then ride it and check A/F throughout the throttle range. Drinking a beer in celebration.

That's really good news! After all the struggle with carbs both you and the bike deserves to get out on the road and have fun.

/Jim

tshrey · « **Reply #644 on:** September 21, 2021, 02:20:47 PM »

Under load the A/F goes full lean (as in the gauge won't read it) and won't accelerate even on flat ground when I tried to run down the street. I'm on the middle clip on the needle. Is the proper next step to go to a larger main or just raise the needle (lower clip)?

RAFster122s · « **Reply #645 on:** September 22, 2021, 08:57:00 AM »

Lower the needle and see where that gets you. Being methodical and limiting changes to one at a time yields better results…just can take longer to get to the end…

Check for air leaks too.

gmoss · « **Reply #646 on:** September 22, 2021, 12:38:54 PM »

Quote from: tshrey on September 16, 2021, 11:10:35 AM

I'm answering my own questions. Those pilot jets are for a 350. If the PO used them who know what emulsion tubes and needles are in it. I'm going to switch everything out to the 4into1 rebuilt components, maybe the needles are wrong enough to let extra fuel from the main jet through.

Funny, I had the exact same issue with my 500. Wonder if there’s some resource that lists the wrong part number or sells the wrong jets in a kit.

tshrey · « **Reply #647 on:** September 23, 2021, 08:55:04 AM »

There must be. The first kit I bought was a rebuild that said for a 74-76 cb550k and after looking at the reference thread on this site showing needle numbers it is quite clearly for a 550F (D274 needle vs D26). So my pilot was from a 350 and the needle and jet were from a 550F. For some reason with that combination it didn't run right...

tshrey · « **Reply #648 on:** October 10, 2021, 02:00:08 PM »

Got the bike running ok with stock carbs but every little change requires pulling them off and I was getting annoyed doing that. Now that I know there is nothing actually wrong with any systems I went back to the VM34 kit. It fits better and is easier to make tuning changes to. Been getting pretty close with that, riding it around town.

If the bike sits without running for a week or so the clutch has been not wanting to disengage with the lever. It feels like it is, but when I tap it down into gear the bike lunges forward and stalls. First time it happened I pulled the clutch all out and checked everything, found nothing. The next time it happened I just put it in neutral, got the bike rolling a little bit and then kicked it into second (almost like a bump start, but with the lever pulled). That worked fine. The latest time I tried it I forgot to check that is was working first and with the bike running dropped it into first. Nasty crunch sound, but it did start working. When I went to drive away from a stop there was a very much non-normal sound from the gearbox. Drained the oil and there are glints of metal in it. So today was pulling everything off the bike in preparation of pulling the motor out of the frame and seeing what kind of damage was done. Electric drivetrain is looking better and better...

wolf550 · « **Reply #649 on:** October 10, 2021, 05:38:53 PM »

it sounded similar to mine when I would leave it for awhile without riding it.
when I start it and it is in neutral all is good and then I push the foot lever down to 1st and loud crunch or clunk sound while shooting forward a little bit before stalling.
I started doing (before starting the bike) roll it out and put in 1st or 2nd gear doing the back and forth oscillate thing which would loosen the clutch disks, put back in neutral, start the bike and when ready to go, pull in the clutch and put in 1st and it wouldn't do the loud clutch crunch.
have not had any problems with it when doing this
I hope your situation is just like this and not something horrible in there.

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Author Topic: 76 CB550 Cafe build (Read 86056 times)