Just bought the bike a few weeks ago 99 wr400 and have not really changed or modded anything. It has ran pretty good up till a couple days ago. Starts fairly easy and runs pretty good with the choke on. When I push in the choke it sputters and pops and dies. I haven't rode the bike but a few trips up the street and back. The only thing I have done is add a brake light and switch. I cant really say what size any of the jets or anything are but I hope someone may be able to point me in a direction to start looking. Like I said before, it seemed to run ok until a few days ago. Kinda all of a sudden is running like crap.