Carbon Buildup at Idle, Erratic Behavior up to 1/4 Throttle

[Guest]

I acquired a 1982 GS550L last year, and after replacing carb boots and fixing some charging problems, the bike ran well. It has the stock airbox and exhaust with 2 holes in the last baffle plate. However this year, even after disassembling the carbs entirely (including from each other) and cleaning (soaking and scrubbing in carb cleaner, using nylon thread to clean jet openings), I still cannot manage to get it running normally. A mechanic near me said that unless I fiddle with the adjustment screws for the throttle sync, unganging them wouldn't be an issue. I've been learning mechanics on this bike, so I'm probably missing something?

The bike will idle while warming up, but then once hot the idle becomes erratic and up to 1/4 throttle feels heavy with the exhaust makes spitting sounds. Anything above 1/4 feels fine though. I've held the idle at 1100rpm so it wouldn't seek, and the plugs quickly started turning from a brownish white to being carbon stained. The only thing I avoided when cleaning the carbs is the air/fuel mixture screw for idle, as I didn't want to mess up the factory ratio, and the setting worked last year. Someone else suggested that a carbs which are out of sync have similar symptoms?

[tom203]

"The only thing I avoided when cleaning the carbs is the air/fuel mixture screw for idle, as I didn't want to mess up the factory ratio"

you'll never get these carbs to run right at low throttle settings, unless you remove the air/fuel mixture screws - the mixture screw is fed by tiny passages that clog easily . It would be hard for any solution to reach these passages if mixture screw is left in place. You can fake a decent idle by fiddling with throttle stop screw, but bike will have crappy low throttle response cuz the low speed circuit is not right.
unganging the carbs will change their sync- at the very least,you'll need to do a good bench sync.

[LAB3]

Totally agree with Tom203! It's not a big deal to pull those out and make sure everythings clean when you do a cleaning. I'd bite the bullet and tear them apart again, chalk it up to earning your future wisdom.

[hampshirehog]

Yep, that's the circuit you're riding on at 1/4 throttle.

[SirKondrael]

Well, I disassembled the air/fuel screws, and counted the turns out for each one before cleaning. 6 - 7 turns out on each carb. It was my understanding from the idle mixture screw tutorial on here that it should be closer to 2 turns out? The bike doesn't run on 2 turns without choke, even once warmed up.

[cowboyup3371]

Make sure you are counting a full 360 degrees as one turn for them

[Wingsconsin]

"turns out" means from the screw fully seated - that is - turned all the way IN
If it took you 6-7 turns to get it out...that is a different measure -
Lightly seated screws are bottomed out in the hole but not TIGHT - seated !
Then you count the FULL (360 degree) turns OUT from that point.

This might seem simplistic - but just to be sure the meaning is correct.

[SirKondrael]

That clarification really helped! Turns out I was counting half-turns and the mixture screws were set only 3 - 3 1/2 turns out. Also, two screws were missing their o-rings and washers, so I just replaced them all with viton o-rings to be safe. I set the screws back to 3 turns out like before, and then after it fouled the plugs realized that the new o-rings were thicker and would affect how many turns needed. It's idling mostly alright now, although during tuning the bike started to falter, twenty minutes idling with a fan blowing across it shouldn't be too bad right?