I stored our Honda 3813 mower in the barn years ago when it was too small for our lawn. I now need to get it going. But here is the problem: Although I have had it running briefly (seconds), it draw through the exhaust and pumps out the carb when turning over on the starter! It does this intermittently with the brief running periods mentioned above. It is as the cam timing is off. I took the valve cover off and the valves are free and not stuck. I also pulled the timing belt shroud back and found the bolt on the center of the cam sprocket not tight. What baffles me is how it could possibly get out of time, then get back in time. The cam timing appears roughly correct when I get a piston at TDC. All comments appreciated.