There are several ways to stop a nitro engine however some choices are better than others. Here are a few methods and some comments on each method:
Pinching the Fuel Line
1 Pinching the fuel line going into the carburetor will stop the engine however it will also cause the engine to rev up and run lean (lack of fuel and lubrication) momentarily before the engine dies. This method works however creating a lean condition, no matter how short the duration, is not the best thing for your engine. Remember that the lack of fuel to the engine also mean lack of lubrication!
Plugging the Exhaust Pipe
2 Using a rag or other item (never use your bare finger as the pipe is super hot) to tightly cover the exhaust pipe outlet will stop the engine but this can cause a build up of fuel inside the engine and may flood it (rich condition). The engine may be harder to start the next time or theoretically, the excess fuel in the cylinder could cause the engine to lock suddenly and piston or connecting rod damage. This scenario is not likely to happen however it is theoretically possible. At the very least, flooding the engine is not a good thing.
Pinching the Air Filter
3 This is the worst method to use as you create the opportunity for dirt to enter your engine. Bad news! Squeezing the filter can knock debris loose and it will get sucked into your engine. Pulling the filter off and using your finger over the carb is also bad as you are giving dirt a chance to enter the engine. Don't use this method!
Contacting the Flywheel
4 Using the back of a small screwdriver or other device to contact the spinning flywheel will stop the engine. This seems to be the preferred method as it does not cause the engine to run lean or rich. Typically, the engine will restart easily after using this method and it is the way, we at BYT, prefer to use. We have found that it is best to use something plastic (like the back/handle of a small, long-handled screwdriver) to contact the flywheel. Be careful to keep your hands away from moving and hot parts when using this method!