Jet Sizes

[Lane]

I have a 77 GS550 with a custom 4 to 1 exhaust built from stock headers and a cherry bomb muffler with a 2'' outlet. I want to up-jet because the bike backfires when rolling at high rpm with no throttle but am not sure what sizes to go to. The shop manual says the main jet is a 80, the air jet is a 1.4, and the pilot jet is a 15.

Thanks, Lane

[Seana23]

Hi babes.
Wow 80 mains!!! They tiddly! Are the carbs Slides or CV's?
What air filter are you using?
Im not sure Bout slides but with CV carbs (and pods) maybe richen up the mixture a little.for idle, raise the needle (if you can) for mid range and go up 2 sizes of Main jet and see what your spark plugs are telling you.
Good luck.
Xxx

[gearheadE30]

That bike has slides fwiw.

Have you done anything to the intake?

Because your setup is custom, it's really going to be a lot of trial and error. If you have only messed with the exhaust, I'd go up 2 or 3 sizes on the mains and go from there. Yours is early enough to have both air and fuel screws, so there is a good chance you'll be able to get away with keeping the 15 pilot.

[gotgixers]

Try a 87.5 or a 90 main, and a 17.5 pilot jet to start with.....You may need to drop the clip on your needle 1 slot.

[BassCliff]

Hi,

New Members, CLICK HERE!! and you'll find all kinds of helpful information on how to clean the carbs, tune the carbs, plug chops, reading the plugs, etc. Welcome to the forum.

Thank you for your indulgence,

BassCliff

[Badooka]

Man that welcome is amazing- I never got one but dang glad I found this info- Basscliff, you website and info is nothing short of AWESOME!