i just got my new yfz 450 a week ago and i am having a problem with it. When i open the throttle really fast in neutral or when i am going slow, the quad usually hesitates and then stalls. Once in a while it will backfire. When i got the quad i took the baffle out and figured that was why it hesitated, but when i put the baffle back in it still hestitated and stalled. I have tryed adjusting the fuel screw, turning up the idle speed, and have also tryed a 48, 50, and 55 pilet jet with no success. Can anyone please help me? Other than this fuel problem the quad runs awsome.

 

The bike is lean stock. When you pulled the pea shooter you made it leaner "hesitates and pops".
Try this put the 45 pilot back in, put your needle clip on the 5th notch from the fat end, change the main jet to a 168 and tune the fuel screw out about 2 turns, this will get you in the ball park. Also run it with the airbox lid off.
Goodluck![img]i/expressions/face-icon-small-smile.gif[/img]