I have a 08 yfz450, I just installed a motoworks sr4 slip on and a jet kit. The quad runs great is fast and idles great. My problem is if I jab the throttle real fast it backfires. If I jab the throttle real fast to full throttle it will die. I have installed a few different jets changed the needle but still the same thing. I have a dynojet jet kit installed so the jets are numbered different than most. Right now I have A 48 pilot, 150main and needle on third groove, air/fuel screw 1.5 turns and airbox lid off. What would cause this too lean, bad plug wouldnt it run bad if it was to lean. I have tried a few different jetting combos and it does the same IM pretty sure it did this before I changed the pipe. I didnt ride it very much with stock jetting and pipe.

 

It will do it even on a properly jetted bike if it's not at running temp. Make sure you not testing this on a cold engine.

 

I fixed the problem with the zip tie mod

 

Hmm. First I've heard of that mod. So from what I read people have problems with bogging down when punching it while riding. I've never had an issue like that.

Glad you got it fixed.