If the engine will not start, or runs very poorly, try this.

[Tornadoman]

I see questions about starting all the time. Here is a mystery that had me baffled. The B&S engine on our rider was not starting. It had fuel, spark, compression. Everything an engine is supposed to have to run. I was dumbfounded. I removed the cover from the top just to have a look. As I was closely examining it I noticed the cutouts for the flywheel key and crankshaft did not line up. So I pulled the flywheel off, and surprise! The flywheel key had sheared. New key, and the trusty old B&S is still running ten years later.

 

[platefire]

You must have smacked something pretty hard

 

[Tornadoman]

You must have smacked something pretty hard

That is why it was such a mystery. It didn't hit anything. Might have been a backfire when shutting down.

 

[Tiger Small Engine]

I see questions about starting all the time. Here is a mystery that had me baffled. The B&S engine on our rider was not starting. It had fuel, spark, compression. Everything an engine is supposed to have to run. I was dumbfounded. I removed the cover from the top just to have a look. As I was closely examining it I noticed the cutouts for the flywheel key and crankshaft did not line up. So I pulled the flywheel off, and surprise! The flywheel key had sheared. New key, and the trusty old B&S is still running ten years later.

Rarely does the flywheel key shear. I mean almost never.

 

[Tornadoman]

Rarely does the flywheel key shear. I mean almost never.

Probably true, but it happened. If you do not know it is a possibility how will you know to check for it?

 

[Diwali]

A few years back I had a similar issue with my B & S on a lawn tractor. The key was distorted (not sheared) in the keyway causing backfiring. It baffled me for a while until I read a post on here. A quick check and a YouTube video soon had it resolved. It’s amazing how much these forums help an ordinary bloke like me!