81 GS450E Misfiring left cylinder only...

[scooterfox]

A) i have a manual...

B) ive already rebuilt them myself which ****es me off that i paid someone else to do it by second guessing myself... im not NEW to rebuilding carbs... just not as confident with this bike as i am with my vespa

C) its not the petcock - i tested it the old fashioned way... sucking on the damn hose... lovely

D) Ive narrowed it down to carbs (most likely) or valves (less likely, but probably contributing..) and have a set of carbs on the way i got pretty cheap.

[matt_gs450]

I didn't see anyone mention the diaphragm within the left carburetor. I assume you and your mechanic inspected them carefully for any leaks. I rebuilt my carbs earlier this year and found that to be the culprit. Once I'd swapped out the bad diaphragm the bike ran much better.

Good luck,
Matt

[nabrams]

Yes, once we start talking about the carbs themselves we can write pages and pages of advice about things to check (like the diaphragm, sticking slide, float needle valve that doesn't seal fully - all these can lead to your symptom) - but it's all been mapped out in detail a million times on this site - do a search.

I can say (as others have) that things I've checked the first time and swore were OK, turned out to be bad on the second or third inspection - usually after ANOTHER full disassembly of the carbs. It's just a reality you deal with if you've been doing this stuff long enough.