400ex Choppy, and Cutting Out

[r-exrider0003]

I have an 01 426, with a hotcam, K&N,jetted, Big Gun Fullrace Exhaust... it usually runs really good, does have a stud broken off at the header so has a minor exhaust leak. Ive never really had a starting problem or reliability problem, but yesterday i rode to church and was running late and was in high throttle the whole way, which probably wouldnt be much farther than 2 miles. But after church was over, i went to take off and started it and it idled fine, but i started taking off and it just cut out and died. it runs fine when your going, i rode it home and it did fine, still has plenty of power, but it fights to idle, and if you blip the throttle it just wants to die. Its kinda running like it would if the choke was half on or something. Idk what this could be, and im about to tear down to clean it and replace some bolts but i was wondering if anyone knew what the problem was, or has had this happen to them. Thanks for any info, i really appreciate it.

[espergre]

sounds like a compression issue due to lack of backpressure. without air velocity you are now pressurizing the cylinder correctly. Sealing the headpipe will also cure most backfiring issues

[QuadManiac]

I'd check to see whether you sucked a piece of gunk into a carb passage or jet. Are you dripping at all from the overflow tube? Could be a partialy stuck open float valve.