The ballast resistor will do it once it's overheated and won't fire until it has cooled sufficiently (once you've experienced it, you'll know the signs) The fuel cut solenoid will do it randomly (usually trying to cross an intersection in an attempt to kill you - had one do that to me, not fun) Maybe the coil is weak or there is something else connected to the ign circuit that is loading the coil up and/or affecting the fuel cut solenoid? Coils last on average 10-15 years max and will cause hard starts, crappy fuel economy and poor acceleration/gear changes. Check the engine tune, make sure your plugs aren't seriously under or overgapped (decreasing the gap by 0.15mm will allow a slightly more aggressive tune) and try experimenting with your timing. The stock tune nerfs most engines and there's a bit of extra performance lurking in there, waiting to be found.