I have this motor in a crafstmen rider that runs great if you can start it. It will crank over until it hits TDC comp and can't get past it. I adjusted the valves to spec per this site and even went tighter on the exhaust after it still wouldn't get over the hump. The decompression does tip the exhaust valve doesn't it? At what point in what stroke does the decompression come into play? Anyway when I had the valve cover off and the spark plug out I watched the rockers to see if they would move on the comp stroke all the way before tdc and way after tdc and they didn't move at all so is the mechanism shot. If so what a shame because it runs great if you can start it. The battery is new and good. It cranks fast with plug out. Is there a starter available with more torque to overcome the bad acr if thats the problem? When I did adjust the valves I went past tdc about a 1/4 per a older post. Help me understand whats going on. Thanks Fred