Topic: CB550 idling problems

[Wyatt565]

Hi all, after a few weeks of researching my problems through this site, I have finally given up and decided to get some tailored advice on the issues with this bike. Thank you in advance for the help, now on to the bike: about a month ago I picked up a sweet 1977 CB550F from a man who claimed to be the second owner. I got it to start and run but only with choke on and the throttle up. It sounded like it had a timing issue so I dug into the coils, found out the guy replaced one coil but not the other. So I did and timing sounded better but the same issue persisted. So I moved onto the carbs, opened them up and they looked pretty clean and rebuilt, I recleaned them just in case. Put it back together and no change. Tore them apart again today and noted the jet sizes: the main is a 115 and the pilot is a 40. Went three and a half turns out on the pilot air adjustment screw and dialed the idle set screw in a little. This time it started and idled. But one you kill the choke it still dies. I have a 4 into 1 exhaust and pods with tape covering about half of them. Any thoughts? Thanks again

[TwoTired]

Have the intake manifolds been off the head?  If so, check those orings.

The carb couplers can also leak.  If hard they can be softened with wintergreen oil.  Be careful not to let them swell up too much.

But really, if it only runs with choke on, I would suspect the pilot jets or the circuit passageways for those jets, including the path to the air jet.

You did remove and clean the emulsion tubes behind the main jet, right?  It's surprising how many reports we get about the carbs being clean(ed), and yet there are bits that were not attended to until the third or fourth try.

I only ran UNI pods on one 550 for a while.  Then restored the stock air box and filter, which most of my bikes now have.  They run so well and trouble free, I can't really understand why people discard the well engineered filter system with cheap not engineered pods.

Finally, have you examined the markings on the choke lever?  Lever down is choke off and normal run position.  Up is choke on for starting cold.  There have been those that assumed the opposite operation.

Done a vacuum sync yet?   Remember to tune carbs only AFTER all the routine 3000 mile tuneup check list has been completed. (Unless you wish to do it all over afterwards.)

Cheers,

[uksparky]

Stock jets were 90 main 42 pilot on 78  550F... TwoTired is spot on.....pods suck   ...going to be too rich 115s...... had same problem some time back, stalling ..idle jets the dam hole is so small.....very thin electrical wire cleaned em out

[TwoTired]

In the US, there was no 78 Cb550F.  Last one was in 77 and still used the early style carbs rather than PD style that the K model used in 77 and 78.
The F had a factory 4 into 1 that swooped around the oil filter on one side and had a quiet/pleasant muffler.
The main for the F was 98 and the pilot 38 for the carb set up 069a stamped on them.  This was the same for all the 75-77 Cb550F models.

Of course, if the exhaust and induction changes, then usually the jetting and main needle settings need changing, too.

The 77 78 K model PD carbs had 90 mains.  But, they also had a different exhaust pressure profile in stock form, and a more restricted inlet on the filter intake snorkel.

Cheers,

[Wyatt565]

Hey guys, thanks for the advice, I had been working on this bike for a few weeks trying to find a solution, then one day before firing the bike up again I decided to test spark again. Upon doing this I found that the coil for 2 and 3 went bad again. Long story short I upgraded to dyna ignition, coils and plug wires.

Now I have a new challenge for you guys. Upon starting the bike up I was practically jumping in glee from how good it sounded and the fact that now it can run with no choke. I shut it down and decided to come back the next day to solve the high idle problem it still had.

I come back the next day and start it up, as I’m feeling the headers I can feel that cylinder one is not getting hot at all. I decided I still had to pull the carb off for a rejet so I would pay extra attention to cylinder one when I did it, so I did but didn’t see anything, I tested spark too and all 4 were getting it, so I threw it back together and started it up.

Now this is where it gets interesting. When I started it this time I found that cylinder one now was getting hot. But now cylinder two is the one not getting hot. Im at a loss. I checked and adjusted all the valves today, they all seemed a little tight. It was adjusted to .002 and exhaust to .003. I also changed oil. Started it up and still nothing on cylinder three, it still idles high between 3000 and 4000. And it still bogs out when you give it a little gas, but a lot of gas will get it to rev up nicely.

Now here are my guesses, for the idle problem it’s the slides, they have been bench synced, but perhaps too high? The bogging down is a fuel air mixture problem in association with not having a cylinder. And the only thing I can think of for the cylinder is a fuel blockage that possibly blocked the first cylinder and when I took the carbs off jostled it into the second cylinder carb? Thanks for reading this very long my post. Any advice would be much appreciated

[Bankerdanny]

Some pictures and additional information from you will be helpful in our armchair diagnosis efforts.

We need to see what kind of 4-1 (and muffler) you have.

You need to confirm what model you have and which carbs. As TwoTired said, a '78 would be a K and have a different carb setup than a '77F.

F model and pre-76 K carbs have a choke lever on the left side of the carb. 77-78 K models have a knob up by the speedometer. The carb model is usually engraved on the #4 (far right) carb buy at the bottom before the float bowl or on the flange where the carb attaches to the rack bracket.

[Wyatt565]

I’m working on getting my photos to post, but the choke knob is on the left side of the carbs. The model is stamped 1977 cb550F super sport pics will follow if I can get them to go

[Bankerdanny]

Ok, that helps a lot.

[Wyatt565]

Here are the pics