I have a 17.5 hp OHV Briggs (model 313707) on an older MTD mower. Years ago the starter was having a hard time turning the engine over to start it. I did some research and discovered the valve clearance needed to be adjusted. After I adjusted the clearance it started like it should. The mower has sat for the last two years and when I tried to start it today it was doing the same thing. The starter will turn it over for one revolution then stop. Turn the key again and it will turn it over for one revolution and stop. I have tried two different batteries, both fully charged and both work fine in other mowers. I have removed the battery cable at the starter and cleaned the connection. I have rechecked the valves and the clearance is what it should be. The oil level is where it should be, no gas is in the oil. If I remove the spark plug the starter spins the engine over like it should. There is some sort of compression issue preventing the starter from being able turn it over. Any suggestions?