Honda GX240 loses spark after running for 30 seconds

Hello, my Honda GX240 on a Lesco Renovator ran fine for some short runs, then was running fine but quit after about 30 seconds.  No Spark, even after unhooking the ground wire so I removed the shroud and checked the ground and plug wire resistance which were within specs, as was the air gap.  It then had good spark, so it started up and ran for a short while before quitting again with no spark.  Any words of wisdom before replacing the complete assembly?  Thank You!