suggestions please

[Xplocivic]

I just got this 400ex and its wicked fast, so I know the jetting is close. Its got a Supertrapp slip-on, K&N filter and I just vented the box lid (for which I haven't changed any of the jetting for, the box lid that is). When I come off the throttle it sometimes bogs down and when I'm going down a steep grade, it will sometimes stall out. Any suggestions on what jet I would need to change or should I adjust the airscrew? Thanks.

[Scro]

You are probably running lean. When you modded the air box lid you are letting more air in, but not getting any more fuel. Try going up on the main jet.

[Xplocivic]

OK, thanks.