Lossing ignition after engine runs?

Check the sideways play on the crankshaft bearing - I had one engine with a similar fault and the magneto was just touching the pickup coils due to wear on the Cshaft bearing
Heat up all the spark components with a hair dryer and see if you still have spark - then if you loose it heat up one component at a time till you find the bad one .....

Tomo
December 2007