Most RC airplane and car engines are two-stroke engines. The engine has a single piston and no valves. Air and fuel are mixed in the carburetor and burned in the cylinder. These simple engines can be very temperamental and difficult to start at times. There are a few steps you should take to help ensure that you spend more time enjoying your hobby than tinkering with your engine.
Prime the engine before trying to start it. RC cars usually have a primer that pumps fuel from the tank to the engine. On RC airplanes you can prime the engine by fully opening the carb and placing your finger over the air intake or the exhaust and turning the prop a few times.
Attach the glow plug lighter to the glow plug. The glow plug has a coil of nichrome wire that heats to red hot with just 1.2 to 1.5 volts of electricity passing through it. This wire is what burns the fuel when starting the engine. Make sure the glow plug lighter battery is fully charged; a weak battery will prevent your engine from starting.
Adjust the needle valve by turning it one half turn counter-clockwise. This will allow the engine to start with a slightly rich mixture. These engines react to temperature and humidity levels and will need to be adjusted before flying or driving.
Use a chicken stick or electric starter to turn an airplane prop over. A chicken stick is a thick rubber sleeve that fits onto your finger or a wooden or plastic stick with a thick rubber coating on one end. Don't try to start a two-stroke airplane engine with your bare hand; if the engine kicks back it could cause injury. Use the RC car's pull start to turn its engine over. In both cases do not remove the glow plug lighter until the engine is running strong. It can take a few seconds for the fuel to flow from the tank to the engine.
Remove the glow plug lighter from the engine. Adjust the needle valve by turning it clockwise; this will make the fuel-air mixture leaner (more air, less fuel). Keep turning the needle valve until you hear the engine start to lose power, then turn the needle valve counter-clockwise a quarter turn.