I have a 2006 TRX 250 EX which has some issues. The carb, jets, airbox and filter have been cleaned. The carb had very little residue in it when I pulled it apart. The engine will only start with the choke on and will rev up but backfires with the choke off and will die as soon as the revs drop. It seems as if the timing chain has jumped the sprocket. I will check the valve clearance and compression. I need some tech info on replacing the cam chain, pulling the head if necessary. The engine sounds good mechanically and doesn't smoke. The rev happy daughter was stuck in the mud. I don't have a service manual but do need a copy of the pages which apply to disassembly of the top end and cam chain replacement. Is the cam chain continuous, have a master link or is it pinned and pressed? Can it be fed thru the tunnel and around the crank? I've done this several times on older sportbikes. Any comments or help would be appreciated.