dwi....there are 3 main things that determine when the fuel will ignite (the ignition point, sort of like when the plug fires in a car engine). Compression ratio, plug heat and type of fuel. You can't do anything much about compression but each blend of fuel has a point where when it's compressed enough it's ready to burn. The more nitro you use then the less compression it needs which means that you have to find a way to delay the ignition (the reverse is true as well). This is done by having a plug that is what's known as "cooler", in other words it has more difficulty getting the mixture to ignite. Some do this by putting the coil in a smaller hole so the mixture has a harder time getting to the red hot coil. Others do it by using a different thickness of wire (or a combination of the two). So playing with different heat range plugs, with the same fuel, is how you adjust the ignition timing to optimum. This optimum is when you have the highest revs at full throttle. However you MUST disconnect the power to the plug when checking max revs or you'll then be forcing the plug to run hotter than it would normally (plus you've got a good chance of burning it out).

As for the stoichiometric ratio using nitro, this goes all over the place depending on how much nitro you use. Methanol is around 6.5 but nitro is about 2.5 so you can see that adding more nitro brings you closer and closer to that 2.5 figure which simply means that the more nitro you use then the further the needles (high and low speed) have to be opened to keep a correct fuel/air mixture. Just remember that any time you change the type of fuel, even oil content, you must readjust your needles to suit.