Jetting a 250ex to the perfect spec

[ozziedodge67]

Hey guys I just bought a 2003 250ex with a fmf slip on and a k&n filter(lid on) and when you turn the chOke on or off it dOnt do much... Seems like when you pull the choke it dies... Also is you rode the quad up to a high rpm and let off the gas it goes ah pop pop pop backfire pop pop .... Running lean??? What jet kit should I go with and what size jets?? Main? Pilot? Needle? And also I got this quad from some one who did not even know how to turn the idle up....

[jshtex]

There are a few simple things you can do to see if it is lean or rich.

1) pull off the air box lid, that will lean it out some. Then see if it runs better. If it does your too rich.

2) With the mods you list if the jetting is still stock I think you would be lean. Ordinarily I would say pull the choke (makes it richer) and see how it runs. But you said it doesn't seem to be working. So if you have a foam filter you could put that on and try it. That would allow less air so it would get a little richer.

3) If the 03 carb has a fuel screw, turning it in will lean it out and turning it out will richen it up.

This may not be far enough either way to get your bike perfectly tuned. But it should help you figure out the direction to go.

Personally I would toss the K&N and use a good foam filter like a Uni.

[trx350X1998]

one thing i always do is get the quad nice and hot, go through all the gears then pull it in straight in the garage. take the spark plug out. what you want to look for is a chocolate brown color on the electrode tip. if it is to light then your too lean, to dark your too rich

[trx350X1998]

the poping could mean too lean or too rich