Size for main jet on GS300?

[Guest]

Sparta seems to be running pretty lean... The spark plugs are bright white even after several hundred miles. She also wants enrichment for a long time when cold, even after idling a minute or two while warming up. She idles fine and will pull away from a stop but tries to bog if I go above 1/3 throttle. That symptom does go away when the engine is warm. Also on hot days she seems anemic but perks up if I pull the enrichment circuit out a little.

After doing some research I have a guess that the main jet may be too small? When I rebuilt the carbs I replaced the main jets with the stock 115 large round Mikuni jets the factory manual called for. But I'm thinking of stepping up to #120. Since jets are around $5 each at the local store I thought I would ask here first. Should I step up more or would 120 make a good difference?

Here is more information...
Sparta is a 1982 Suzuki GS300LZ. The carbs are Mikuni but not sure what model. I use pump gasoline and it does contain ethanol in my area. Everything is stock except the mufflers which are EMGO dunstall reverse cone with the metal baffles. The carbs were rebuilt with new jets, O rings, needle and seat, and the bodies ultrasonic cleaned about a year ago.

Thanks in advance!

[tom203]

Maybe the ultrasonic didn't get pilot circuits clean enough ,so bike is somewhat fuel starved in mid range.try a bigger main jet and/or shim needle up a bit .

In this same forum, member jbowles has some gs300 questions - maybe you can steer him.

[BiomedDR]

Down low there isn't any issues. In fact if I leave the enrichment circuit out the idle ramps up and starts to run fat. I think I will try #120 mains and see where that gets me.

I will also post in jbowles thread with all the info I have.

Thanks