doesn't seem to be running right

[zzsa02]

I have a 05 450 I just put a pipe on and rejetted didn't run very good so I started playing with jets and got it to run great from 0 to 3/4 throttle 3/4 on it will start dieing out and running badly if I take the airbox lid off it would great so I would assume that is running out of air so I lean up the jets ended back to stock still doing it put the stock pipe back and still does it. didn't do it before. Is okay to run with the lid off in a hare scramble race that is this weekend. Does anyone know what could be causing this?

[jshtex]

I don't know about your problem but as for running with no lid, we ran a yfz for three seasons of xc racing with no lid and a foam filter.