Two stroke motors are widely used in a variety of machines due to numerous advantages over four strokes (namely, fewer moving parts, lighter weight for the same horsepower, less maintenance required, etc.) Because of the lack of valves controlling the intake and exhaust, back pressure is very important in these engines. An exhaust pipe full of carbon deposits can reduce the overall performance of your motor; if you have a two stroke dirt bike or scooter, follow these steps to make sure you are not being robbed of precious horsepower.
Pull the pipe out.
Be careful not to damage the gasket between the cylinder head and the exhaust; if you do, you will have to replace it; it won't do to have gases escaping from this union.
Plug one of the openings of the exhaust; you have to create a good seal here, sometimes wine bottle corks work well, but don't use any tape, as the cleaning chemical you will be using will break it down completely. Now, spray a whole can or two of brake cleaner inside, then plug the other opening; sometimes there is a secondary opening on the side of the pipe, or a "slave tube", plug these as well.
Slosh it around and let it sit for a while; then, slosh it around again and let it sit in a different position; do this as many times as you can and if possible allow the chemical to work overnight. While you are waiting, you can take a look at the exhaust port on the cylinder head, if there is build up here too, clean it up VERY CAREFULLY with a little brake cleaner and a rag; turn the engine so that the exhaust port is covered by the piston, that way you'll avoid pushing deposits into the chamber; don't use a screw driver, as you could damage the piston.
Before removing the plugs, tap the pipe gently a few times with a hammer, then pull out one of the plugs and pour the slush into a pan (make sure to discard it in a responsible manner.) All the carbon build up should now be out of the pipe and into the pan. Try to drain all the chemical out of the pipe and don't install it before it's dry on the inside. Now remove the other plugs.
After all the chemical is out and the exhaust is dry, you can put it back in the machine. The engine may smoke a little more than usual at first, this is due to the residue of brake cleaner getting burnt off; make sure you run your machine outdoors or in a well ventilated area. Make sure also that there is a good seal between the exhaust and the cylinder head.
Without resorting to aftermarket and performance pipes, which manipulate the back pressure for different results, keeping a clean exhaust is most important in two stroke bikes; it will ensure you have proper low end torque and acceleration.