I think you will find it is backfiring, you may want to check the
timing/points.

wrote in message
...
I have this snowblower, it is an old one, tecumseh engine. It has
good spark , until it turns over and fires and the flywheel key shears
off. When I pull with the plug disconnected there is no issue. As
soon as the engine fires it shears the key. Do i need to adjust the
valves etc?

Thanks