I never had much trouble starting them, either, if they don't start you're either doing something wrong, usually flooding it, too much fuel, or it's a bad glow plug.
Glow fuel is mainly methanol (methyl alcohol) with around 20% castor oil and 0-30% nitromethane. The smaller engines need more nitro, I thin Cox fuel was around 10% and the "Cox Racing Fuel" somewhat more.