My grizzly just died backing it off the trailor. I have tried adjusting the valves they seemed a bit tight because when i first started to line up the timing marks you could only turn the motor over so far then it would stop, would this be because the piston was touching the valve? I loosened all the valves way up and then i could turn it over easily. So i put them into spec and tried to start it and it is backing firing through the intake. It did back fire through the intake even worse before this. What am i missing here. Any help would be great.