If you have a service manual put it back together and time it right, its not hard to get a 4 stroke motor 180 out, it can happen on car engines too. If I think I am right that spark should happen at certain time on the flywheel, the cam should have a certain amount of turns to one turn of the crank, if its timed right it should spark with one turn of the flywheel, the cam should turn around 3-4 I think with one turn of the crank. If its got a hell of a spark and its spittings or blowing fuel back out the carb I think its timed wrong the intake is slightly or full open on the compression stroke.