Honda Lawnmower Engine Won't Start Woodruff Key is Okay

My craftsman lawnmower with a Honda engine won't start. It quit while I was mowing the lawn. I don't think I hit anything. It sometimes backfires when you try to start. I pulled the flywheel and the woodruff key looks good. Any suggestions would be appreciated.

 

Put in a new spark plug. Otherwise, check for spark and check valve timing.

 

When I pull to start there is less resistance then before it stopped working. How do I check valve timing?

 

Pull the plug and have someone rotate the engine and feel if you get suction, then exhaust - the indiction of decent enough compression. Can you look in the plug hole with a bright penlight and see the piston go up and down and/or also the valves fully open and close, on that particular engine?

 

This engine should be timed by a timing belt, so the valves opening and closing and piston moving is good, but you must verify that this is happening at the right time. Remove the valve cover and observe the rocker arms, the push a pencil or drinking straw into the spark plug hole as far as it will go. Slowly turn the engine. Watch the rocker arms and the straw. There will come a point when one valve closes at the same exact moment the other begins to open. At this point, the piston should be at the very top of it's travel as indicated by the straw. It must be exactly at the point between moving up and down at the exact moment the two valves change movement. If this is how it works, then the timing belt is ok. If not, the timing belt has slipped. If the piston doesn't move at all, the rod is broken (engine blown).