My buddy has a 08 yfz 450 that boggs when you first punch it and almost backfires. We have changed out the jetting, rebuilt carb, had it dyno tuned... you name it.. I cleaned the gas tank, replaced fuel lines. etc etc. One weird thing is the quad runs fine when the choke is out... even when the quad is super warm after running for an hour it still has the same issue. Runs fine with choke out, runs like crap with choke in. Has this happened to anyone or does anyone know how to fix it?