idling problems on cb550, please help

[tom_b]

Hi all
I am fairly new to this and I have got a 1977 cb550f2, when I was buying it I knew it will need some work to it.
So far I've rebuilt the carbs using the repair kits and the problem I have is that the bike does not idle when I close the choke,
the only thing I'm not 100% sure is the float heights and if they are correctly synced, anyway I've checked for any vacuum leaks and tried different positions with the air screws, but still no success.

also I've noticed smoke blowing out from the front of the exhausts, where it joins with the engine, not a lot but still was wondering does it have any effect on this situation? I suspect I'll need to change the gaskets.

So any help would be appreciated!
Thanks

[Ashdowner]

You have lots of sympathy because you're not alone. Are they the P46 carbs? If you've rebuilt the carbs then we'll assume they're airtight but you need to get those gaskets sealed at the exhaust outlets before you go any further because that will affect it. After that, timing is critical as are float levels. Check valve clearances. Assume you have a petrol filter on to collect the rubbish. Does it have the original exhaust system and if not are the jets different from standard? Do all the plugs have the same colour? I put electronic ignition in my K3 and vacuum-synched the carbs which helped a little but I can't get it to tick over below 1400 without the clutch side sounding like someone dropped a bag of nuts into the gearbox.     

[tom_b]

Thanks! But I think the problem that i have is that one of the cylinders is not working, I might need to replace the ignition coil, because there is no change when I unplug the spark plug cable, also that side is much cooler that the other side.
So I'll try to sort this out this week and then see if everything is alright.

[SteveD CB500K0]

If just one cylinder is cold it is the carb not the ignition. The coil drives two cylinders using the wasted spark system.

Steve

[tom_b]

But when I swaped the cables around with no2 cylinder, and tried unplugging it again, then it seemed to be working, could it be the cap?

[Chris400F]

Have you tried swapping plugs between cylinders? I haven't seen this mentioned so far, should be an easy thing to try.

[tom_b]

Yeah i kind of thought it can't be the coil, so I ordered the cap, but I'll try swaping the caps between no4 and no1 later this evening, I'll also check the sparkplug.

Thanks for the info everyone, it's really useful!!

[mihai.i]

I had almost the same problems with my CB550k 1978. Rebuild the carbs, timing, valve adjustment and carb sync but idle was way off..and the cyl 1 somethimes not fired.

Turn out there was a bunch of causes:
1- there was some air leak ant cyl 1 and 4
2- the timining was not ok..i discovered only with the strobe light...i removed the advance cleaned, put it back, retimming with the strobe..is ok now
3- i changed all the sparks plug and spark plug sockets (NGK)
4-I got low compression 7-7-8-8..its a bit hard to start in cold season but during summer in ok

The main reason for not idling was the air leak, and the main reason for not firing cyl 1 was bad timing!

[Ashdowner]

Mihai, how did you find the air leaks and where exactly were they?

[tom_b]

So...I still can't get it to idle good.. previously i said that cylinder 1 was not firing properly, and 2 of the carbs were leaking over night so I've changed the ignition coils which seemed to help and it seems to be firing better now but still less hot than the right side, and also the carbs don't leak no more, assuming that the cylinder is burning off the petrol now? I've checked the velvet clearances and adjusted them (also should there be oil under the tappet screws? where the rocker arms are?) I've checked the timing using a timing light with alligator clips and noticed that the light lights up before the F 1.4 mark reaches the index mark, but very close to it, checked the breaker point gaps and they are between 0.3 to 0.4 mm, which is by the manual book.
I can't really check for air leaks because it does not idle same all the time..
once i close the choke there is a lot of white smoke, but i need to keep playing with the choke because it dies on me otherwise,
but started it a bit later and it wasn't smoking white smoke anymore, just a little black when revving it, and it revs really hard, as if there is no power and is choking....
anyway would a video help if I would film it??

Thanks

[tom_b]

Anyone? Im sorry for being a pain in the butt... 

[royhall]

You say 2 carbs were leaking overnight? Were they leaking from the drain hoses/air filter or the bodies? If its the drains they are not shutting off on the float valves which would probably cause your problems as the fuel will be way too high in the 2 leaky carbs.

Are you leaving the fuel tap on overnight?

Also, you will need to set your timing with a strobe to get it accurate and be able to check the advancer for correct operation.

But you will need to sort the carb leaks before you can go any further, as overfilled bowls will cause havoc with your running.

Good luck with it.

[tom_b]

Sorry for being so confusing,  I realise now that I should not have gone straight into rebuilding my carbs until I've researched more...
Anyway, I haven't done anything with the timing and the 2-3 cylinder was the same.
And the carbs are not leaking anymore since ive changed the coils, I think one of the H.T leads were bad...
I went for a ride today, it was a struggle to keep it from switching of but it rode for a little, and then i braked with my back brake and it sort of just died and could not start it up again, even with the jumping leads (the battery is pretty bad) could there be an electrical fault for it not being able to start?
Thanks

[Johnwebley]

get the battery charged,

 check the plugs for colour,and gaps,

 and start from there,

 whats the air cleaner like?  clean or dirty

 

[Ashdowner]

Get the timing right. Points gap ok? Condensers ok? Which carburettors do you have? Are the float levels correctly set?  is the exhaust original or aftermarket and if so are the jets the correct size? Are the needles in the right position? Are your throttle and choke cables correctly adjusted?  Are the carb slides synchronised to start off with? Are the carbs properly fixed with no manifold air leaks? What is the lowest rpm that it will run without dying and is the throttle stop screw set below that? When it died on you and wouldn't restart, did the starter turn over well or did the battery appear to be flat? Were you on headlight at the time? If flat then get the battery tested and check the alternator output. What colour are your spark plugs, and if they're all a very different colour then that should tell you something about the carb adjustment? Is the air-filter clean? Is there an-air-filter there? If you can get it running then get hold of some vacuum gauges to check the carb balance. You have to do all the basic checks to eliminate the potential problems one by one which hopefully (but not always) will lead you to an answer.