A couple of months back i took the head of my kodiak 400 to have the valve seals and guides done as it was burning a bit of oil on over run. When i put it back together first time it started instantly and ran for a few seconds then stopped... the cam chain had somehow come of the bottom cog in the process and i hadnt noticed. It did no damage to the valves or piston but now ive put it back together i cannot get it to run it just backfires ive been messing about with the timing all day and im at a loss with it. I feel like ive adjusted it in every possible area but still no luck. What else could it be. I have spark and fuel seems to have compression.... HELP!