Jetting HELP!

[ill_lil_romey]

Ok guys listen up. I just removed the choke from my 400 ex carb. There is great throttle response and added gitty-up throughout the powerband, the problem is, at idle and in the lower rpm,s the carb jumps and the bike spits and sputters. Not much , but noticable. My altitude is 4 feet below sea level in southeast louisiana. I need help. Is this a jetting problem? Seems like one to me, but what do I need to do to solve it? The bike has a WB R4 slip on and a mod air box. Uni foam filter.

[ill_lil_romey]

BUMP

[tprender]

Did you up the pilot jet and/or what size is in the carb now? Need more info. (filter, pipe, exhaust, or stock engine)

[AtvMxRider]

Yeah what size pilot jet are you runnin.

[ill_lil_romey]

The only mod to the carb was the choke removal. It has the welds ground out ot the headpipe and ceramic coating, a white brothers R4 slip on, 5 1inch holes in the air box and a uni foam filter. the jets are all stock. the choke removal was the most recent mod and since then the problem has arised.

[Ketch]

For jetts you should be some thing like this #40 pj. needle 4th
grove from the top #155 to #165 mj. Air screw out 2.5 to 3 turns out. this should get you close.:)

[GoLikeHell]

Originally posted by ill_lil_romey
The only mod to the carb was the choke removal. It has the welds ground out ot the headpipe and ceramic coating, a white brothers R4 slip on, 5 1inch holes in the air box and a uni foam filter. the jets are all stock. the choke removal was the most recent mod and since then the problem has arised.

Doesnt White Brothers give you a jet size to use when installing a pipe? I dont know since I never bought a aftermarket pipe.


Mark

[ill_lil_romey]

I've heard that the only real need for the 40 or 42 pilot is for ease of starting. Just recently someone told me that if I turn out the air screw and put the needle 4th groove that it may fix the problem. I guess its a trial&error process. Trying to get perfect jetting is a pain in the ***!

[Steve-o 400EX]

Originally posted by GoLikeHell


Doesnt White Brothers give you a jet size to use when installing a pipe? I dont know since I never bought a aftermarket pipe.


Mark

Yea but since he removed the choke, this changes his setup so he will need different jets than what the instructions say.

[stupid driver]

Originally posted by ill_lil_romey
Trying to get perfect jetting is a pain in the ***!

aint that the truth

[GoLikeHell]

Originally posted by Steve-o 400EX


Yea but since he removed the choke, this changes his setup so he will need different jets than what the instructions say.

But that should get him close, then add fuel. According to his first post he has stock jets in the bike. His bike really needs a dyno run to show where is a/f really is. ill bet his bike is running way too lean and could result in piston damage. I know im the guy who screams run it lean and mean, but running it too lean is not good. I just rebuilt a bike for a buddy that was tuned by a shop that didnt have a dyno. damn thing was 12-1 a/f at idle ( fat) then once you floored it the bike would puff black smoke. But once the puff of black smoke was gone the bike shot the a/f off the scale! So after a new piston the bike was tuned properly and ran some low 30 hp runs with no porting.

Mark

[Steve-o 400EX]

Originally posted by GoLikeHell


But that should get him close, then add fuel. According to his first post he has stock jets in the bike. His bike really needs a dyno run to show where is a/f really is. ill bet his bike is running way too lean and could result in piston damage. I know im the guy who screams run it lean and mean, but running it too lean is not good. I just rebuilt a bike for a buddy that was tuned by a shop that didnt have a dyno. damn thing was 12-1 a/f at idle ( fat) then once you floored it the bike would puff black smoke. But once the puff of black smoke was gone the bike shot the a/f off the scale! So after a new piston the bike was tuned properly and ran some low 30 hp runs with no porting.

Mark

That is true, good point.:blah