Howdy all, got a question about a problem I've had a few times now, my intake valve will get out of adjustment for no apparent reason. It normally does it when trying to crank it for the first time. The engine will spin over and hit then I hear a pop or backfire through the carb. I start again and the engine spins fast because the valve never closes to make compression. I open up the top and the adjustment nut is still tight but there is 0 clearance. It happened this past weekend while riding. It was sitting still idling when it happened. Any thoughts would be greatly appreciated.