My belief is that if it fires with fuel down the plug hole the motor has not been straight fueled. The way to test the decomp valve is to take it out, put a piece of tube on it and suck on it, if the valve shuts it is fine. The other thing with a mower returned with an empty tank is often caused by the float needle not shutting and the fuel ending up in the crank. This is not the case with this one as it fires with fuel in the plug hole, if the sump is full, it will not fire. You can check the compression by removing the decomp valve and put a spark plug in the hole and see what it is like to pull over. These motors will run with quite low compression.
