Have pulled valve covers and valves are opening and closing. No bent push rods, etc.
Can put fingers over the plug hole and crank the engine. Can feel suction and exhaust pressure.
Will physically pull the flywheel and check the key. Looks fine, but have not actually pulled the flywheel off...
I have an MTD rider with a 25 hp Briggs. Mower was running fine. At the end of last season I replaced the main drive belt. First start attempt after belt replacement resulted in a back fire. Second attempt started up fine.
Drove tge mower to verify the belt was good to go. Parked the mower and...