WARNING Just like full-size motorcycles, pocket bikes can be very dangerous. Only drive a pocket bike with your parents present, always wear a helmet and always wear protective clothing. If you fall off going 40 MPH, you will be glad to have a layer of clothing and the shell of a helmet between you and the road.

This pocket bike is a small motorcycle stripped to its most basic pieces. It's two feet high, weighs 50 pounds and can go 40 miles per hour!

When we took it apart, here's what we found:

The gas tank is filled with gasoline, with a little bit of oil mixed in to lubricate the engine parts.

The carburetor pumps air in from the atmosphere, mixes it with gasoline from the tank, and feeds the mix to the engine.

The heart of the carburetor is the throttle plate -- a movable flap, controlled by the throttle on the bike's right handle. Turning the throttle opens this flap, letting air into the carburetor. More airflow let's the carburetor send more gas to the engine.

This bike uses a two-stroke gasoline engine - the same type used in chainsaws. Inside the engine, you'll find a combustion chamber, a spark plug, and a moving piston connected to a crankshaft. In each engine cycle, the spark plug ignites the fuel in the combustion chamber, creating an explosion. The explosion pushes the piston down and back up again, turning the crankshaft.

The crankshaft connects to a centrifugal clutch. The clutch has an outer drum, a central shaft, and two weights attached to the central shaft. When the central shaft turns slowly, it spins separately from the outer drum. When it spins more quickly, centrifugal force pushes the weights outward. The weights lock onto the outer drum, and the central shaft and outer drum spin together.

The outer drum of the clutch is connected to a chain, like the chain on a bicycle. The outer drum turns the chain, and the chain turns the back wheel.

The brakes are called disc brakes. Disc brakes work a lot like bicycle brakes. When you squeeze the brake handle, it pulls on a metal cable, which closes a clamp. The clamp grabs a metal disc connected to the wheel, and stops the wheel from spinning.

And here's how it all comes together:

Opening the throttle plate just a little turns the central shaft slowly. Only a little gas and air can get into the engine, so it cannot go very fast. The weights don't connect with the outer drum, and the bike idles (no power reaches the wheel).

When you open the throttle more, more gas and air flow into the engine. That creates more power. The central shaft spins more quickly. The weights push out and grab the drum. The drum spins with the central shaft, rotating the chain. The chain turns, spinning the rear wheel and the bike takes off.

When we get cool things like this pocket bike, you know we just have to check it out. For photos of the test drive, check out the following page.