I have a 400EX with the 440 kit. It has sat for a while now and I started to clean him up to ride. Well first off, the intake mani was leaking, so it was backfiring and sputtering bad. I replaced that and cleaned the carb. I put a new plug and fresh gas. It started up right away and idled smooth, and reved nice. So I tried to ride it and when I put it in gear and try to go, it sputters and barely wants to move IF it does move. When I stop trying to move and just rev the motor, it revs fine. I think I have a 185 or so jet in it, with the CDI box, a stage 1 cam and FMF pipe. It looks like I have some oil between the head and jug, so maybe a blown head gasket, but would that do it? I can't finger it out, so any help would be great.