A friend just bought 95 bayou300, not running.Was not firing, changed cdi and rectifier, now firing but wont crank, blows raw fuel back out of carb(small fire!) He adjusted and we checked valves intake .005 exhaust .007 Timing mark on botom(through site hole)is on the line beside the T. the top mark is close to the 300 on cam gear(one tooth is slightly left, and one tooth slightly right)key ways are tight not wallered out, am guessing chain must be stretched a little, piston is at tdc on comp stroke. anyone have any idea what could be wrong??? thanks for any help  

have you tested the compression.
sometimes when the rings are worn they can leak compression back through the carb.