Some people convert glow engines to spark ignition. This is possible with battery powered electronic ignition modules that use hall effect sensnors to trigger the spark. They even make spark plugs with 1/4x32 threads that fit right into glow plug holes. Large 4-stroke engines converted to spark will reliably idle at rediculously low rpm and need no nitro. While you can convert a .40 to spark, the extra weight of the ignition system is not worth it, and you will still need to feed the engine a fuel blend that is about 20% oil.