I bought a building recently and a Deere 125 riding mower with only 167 hours was part of the deal. It ran well but about 70% of the time would not start when the key was turned. The previous owner would open the hood, turn the motor fan disk over the compression hump and then use the starter to start the engine.

Yesterday I adjusted the valve lash for the intake and exhaust valves and now it starts beautifully. For anyone having this problem, go to YouTube and search on Briggs & Stratton. This fellow's video is the one I followed: Lawn Mower Repair Valve Adjustment V-Twin - YouTube