Check your Carb Joint for cracks..

[YZ250F49]

My sons 03 250F was starting to backfire and then would not start or run w/o the choke on.

I looked down at his carb and noticed his rubber carb joint had a large split in it causing the problem.

This is also an excellent way for dirt to get in bypassing the air filter and trash your engine.

I think the clamps were overtighened from the factory causing the split, as I do not recall ever touching them.

You might want to check yours.

[streetndirt]

I thought the clamp for that had a spacer that kept it from being over tightened.

[YZ250F49]

Yes, there is a spacer, but I don't know how it could have cracked otherwise.

[Kawasami]

Same thing happened to me but it was my own fault. I did not notice that the clamps should be aligned with the taps on the rubber and after one ride the rubber was torn.

Sami

[oldnbold]

I didn't know my old carb joint was being recycled. I thought I threw that thing in the trash. ?

Seriously, mine had a crack twice that size.

[streetndirt]

I'll be checking my clamp alignment tonight for sure.