[rotorwrench]

One thing I've seen happen a time or two is when something gets into the gas tank that can slowly get drawn to the outlet pipe and block it. This kind of stuff will drive you crazy till you find it. Once the engine quits, the bugger falls off due to lack of suction draw and then the engine will run again for a while. The only other thing I can think of would be a temperature sensitive problem such as a coil with a cracked wire winding. It gets hot and the crack opens up but the gap closes back up after cool down. This stuff will wear you down sometimes.