I recently purchased a used Craftsman Riding Mower. This mower has a Briggs and Stratton 17hp OHV motor. I went to start it tonight and it cranks really, really slow and doesn't start. I did a little internet searching and came up with pulling the spark plug to see if it cranks. Once the spark plug is removed it cranks really well (like normal), but when I put the spark plug back in the engine cranks really, really slow again. I believe it to be some type of compression problem....perhaps too much compression? Honestly, I don't know what to do and how to find the problem. If anybody has any ideas on what I can try, please let me know. I'm debating on getting a socket to fit the nut on top of the engine and try to start it with my impact air gun but don't want to mess something up. TYIA.