quick carb ?

[450raider]

can someone give me a quick rundown of what a pilot jet, main jet, idle screw, pilot needle, main needle and what this stuff looks like and the function of it and whatever else i might be forgetting because my brother has a small bike that we put a t4 slip on on it and now it backfires alot and (takes forever to get warmed up although thats not a big issue) any help will be appreciated.

thanks

[ghott]

I believe this is how it goes on a 450R 42mm Keihin. Not sure about a smaller bike...but here goes:

Idle screw = adjust the idle speed
Pilot jet = Idle to 1/4 throttle
A/F mixture screw = 1/4-1/2 throttle
Needle = 1/2-3/4 throttle
Main jet = 3/4 - full throttle

Some overlap on each, and a good A/F mixture also compliments everything as well.

If you are popping on decceleration, the pilot jet or A/F mixture is probably to blame due to a lean condition. Adjust the A/F mixture out a 1/4 or 1/2 turn out at a time. Or, go one up on the pilot jet.

Good Luck.

And if any of this info is wrong...correct me please.

[GPracer2500]

The fuel screw (aka: pilot screw, A/F mix screw, slow circuit screw, etc.) is part of the pilot circuit (the dominant circuit between 0 - 1/4 throttle).

here

one more

[450raider]

well its for my ttr and i found out it has a

40 size pilot jet &
130 size main jet


so is one fore air and the other for gas? and if so then i should go one up on that?

[GPracer2500]

Originally posted by 450raider
well its for my ttr and i found out it has a

40 size pilot jet &
130 size main jet


so is one fore air and the other for gas? and if so then i should go one up on that?

They're both for fuel. Carbs use different jets to provide fuel at different throttle openings. The pilot circuit (which includes the pilot jet) provides the fuel from about 0 - 1/4 throttle. The main jet provides the fuel from 3/4 - wide open throttle. In other words, at 1/4 throttle (and less) the main jet size isn't factoring into the fuel delivery very much. But at WOT the main jet is providing almost all the fuel being used.

Both circuits could probably use a little richening with the slip-on.