ok guys, im asking this question to help my buddy out who has a 02 yz426f. yesterday we riding and after about an hour we went back to the trucks. when he went to restart it, it fired right up, but when he gives it some throttle it just bogs down, kinda like he's trying to take off in 4th gear. we checked everything and it seems to look ok, but too scared to open it up and really look. any suggestions on what it might be?