My buddy was mulching leaves and doing the last mow of the season with his Cub Cadet rider with Kohler Courage 20hp when it died. It acts like it is out of time. Try to crank, it hits a spot and stops. Not mechanical contact type stop, but compression. Put jumper cables on it and still the same. If I help it past TDC by turning it slowly by hand, it will crank over a couple times and seems to be backfiring. Couldnt tell if through intake or exhaust. Is there a common problem I should check first like the keyway or something? I plan on starting with a compression and leakdown test.. any direction much appreciated.