So, how big is your lawn?

Flat head engine 4 stroke engine? If so I would remove the head clean the carbon from the combustion chamber (head, valves, top of piston, head gasket, and spark plug) and look for slop between piston and cylinder wall.

2 cycle? WTFO probably.

I have one that did that many years ago. It was bad electronic ignition coil (if that's the right term). Replaced it and its' still going strong.

Thanks for the replies.

Mike, the yard is very small and the LB is used as my trim mower. I use a small lawn tractor for most of the work.

rcmoser, the LB is a 2 cycle engine, F series I think.

whizzer72, I expect the same as you; i.e., the warm engine changes the coil characteristics so the spark isn't as strong. Just hate the cost of a new coil for troubleshooting.

I agree with whizzer, The way to find out if the module is not working is to disconnect the spark plug wire, remove the plug , reconnect the plug wire .then with the plug touching a bare metal spot on the mower, pull the starter cord and see if there is a spark. If no spark, it's the module.

I'll try the spark test suggested by bogman to see if I have spark. If not, could it possibly be a bad spark plug?