82 GS550L running poorly at high rpm... suspect carbs

[Anonymous]

Hi,

I have a 1982 GS550L that I'm trying to get running properly. From searching the board I've managed to clean the carbs and get it to idle ok and run ok at lower rpms. It will rev up pretty well when in neutral also, but under load it has some hesitation and starts cutting out aroung 6-7k rpm. I suspect it leans out but I can't say for sure... The main jets are all clean.

I'm not sure what the screws at the top of each carb do on this bike... I currently have them each turned out 3 turns. high rpm seems to be a little better like this than with them further in, but not by much. the hesitation seemed less with 2 turns, and it didnt seem to hesitate at all with them turned all the way in. I was about to try turning them out further but I'm tired of taking the tank on and off and figured i might be better off trying to figure out what they actually do before i waste more time messing around with them. anybody know?

Thanks,
Jeff

[robinjo]

Re: 82 GS550L running poorly at high rpm... suspect carbs

Hi,

I have a 1982 GS550L that I'm trying to get running properly. From searching the board I've managed to clean the carbs and get it to idle ok and run ok at lower rpms. It will rev up pretty well when in neutral also, but under load it has some hesitation and starts cutting out aroung 6-7k rpm. I suspect it leans out but I can't say for sure... The main jets are all clean.

I'm not sure what the screws at the top of each carb do on this bike... I currently have them each turned out 3 turns. high rpm seems to be a little better like this than with them further in, but not by much. the hesitation seemed less with 2 turns, and it didnt seem to hesitate at all with them turned all the way in. I was about to try turning them out further but I'm tired of taking the tank on and off and figured i might be better off trying to figure out what they actually do before i waste more time messing around with them. anybody know?

Thanks,
Jeff

The screws on top of the carbs are for the micture at idle, adjust them per carb for the highest idle and leave alone for the rest. Set idle at about 1000-1200 rpm, did you synch them yet?

Do you have the stock airbox on, hooked up to the carbs with no air leaks and a clean filter?

[gspaul]

1 1/2 - 2 turns out is the area you should be in( as long as you have no mod's),and robinjo is right it only controls about the first 1/4 of throttle.
Have you checked for air leak's between the carby's and the head?A fine water mist when sprayed on will cause a misfire.
Is it a standard air filter and is it clean.
When you have had the carb's apart they must be synch again.

[KEITH KRAUSE]

A bike that rev's when in neutral but not well under load is usually lack of fuel.
You say the carbs are clean and main jets too. Did you inherit the problem or did it just start happening? The float levels may be off. Any "high idle" problems? Does the bike idle much higher once warmed up than when cold? If so, intake leak. Both these things would cause your problem.

[Anonymous]

more info
I inherited the problem. The bike would only run on choke and would not rev at all when i got it. Intake manifolds are brand new, airbox is on and filter is clean. Carbs are not synched but I did not take them apart from each other. I have not set the floats either. (I guess setting the floats will be my next step)

When i had the idle mixture screw all the way in, i could hold the throttle fully open in neutral and the bike would fluctuate between 4k and 7k rpm, as if it leans out at 7 but gets enough fuel again when it drops to 4. choking off the air box intake lets it rev smoothly to 10 in neutral. It seems to me like it is only running off the pilot jets but I don't understand how that could be possible.

does the idle mixture become more rich or more lean when turning out the idle screw?

just to clarify, the procedure to adjust these is with the engine running, adjust each one individually to the point the idle is fastest? then turn down the idle speed adjuster? any particular order or just do left to right?

Thanks for all the replies
-Jeff

[KEITH KRAUSE]

On your carbs, turning the screws out will richen the mixture.
Your screws were probably about 1 1/2 to 2 turns out from the factory. The motor/carbs must be in good operating condition for the screws to effect the rpm's correctly. That means no intake leaks, compression problems, the carbs must be completely clean, float levels correct FIRST, good spark/timing, etc. The screws are last to be set and then the vacuum synch. You can initially set the screws to about 1 1/2 to 2 turns for starting purposes.
Since you don't know the history of service on the carbs, take nothing for granted. Basic checks should be done first to make any trouble shooting easier.
If you're positive the carbs are clean, then set the floats and re-check for any dirt/varnish while you have the bowls off. Be sure any screens above the float valve seats are clean. Keep each float valve with its seat. Don't mix them up. Be sure all o-rings look good inside. Be sure all jets are tightened firmly. Note the size of the main and pilot jets and be sure they're the correct sizes before putting carbs back together. Verify their sizes here if not sure. If your manifolds had o-rings, replace them too. Be sure your vacuum line is in good condition. Be sure the gas tank vent is cleaned out. Be sure any in line filters are flowing well. Then you must bench synch the carbs and follow that with a vacuum synch.
Adjusting the mixture screws for highest rpm: Turn them out to about 2 turns before starting. Place bike on centerstand and warm up completely. Set idle to about 1,000/1,100 rpm's. Starting at any carb, slowly turn the screw in either direction and listen for the highest rpm. Find the sweet spot. Stop turning as soon as you hear the rpm's max out. Now lower the rpm's to 1,000/1,100 rpm by using the idle adjuster knob. Repeat this to the other three carbs. When done the bike should idle properly at 1,000/1,100 rpm unless the bench synch was done wrong. Now vacuum synch.