Better magneto images

The Magneto

The magneto is an alternating-current generator that contains a permanent magnet. A magneto requires no source of direct current for its operation. The most common use of magnetos is in the ignition system of some internal-combustion engines. Magneto ignitions are used in lawn mowers, snow blowers and other 2-stroke engines; they may be used in vehicles—including certain tractors, snowmobiles, motorboats, motorcycles, and small airplanes—that do not require storage batteries to operate auxiliary equipment. Like the storage battery in an automobile, the magneto provides the electric voltage that causes the spark plugs in the engine to spark.

The two main parts of a magneto are a permanent magnet and an armature. The armature is a piece of metal around which is wound the primary, a coil of a few turns of heavy wire.

In most magnetos today, the armature is stationary and the permanent magnet rotates; in others, the permanent magnet is stationary and the armature rotates within the magnetic field produced by the magnet. The relative motion of the magnet and armature generates an alternating current in the primary.

In the typical magneto used in an internal-combustion engine, the magnet is turned by the crankshaft of the engine. The voltage generated by the magnet in the primary coil is not sufficient to cause a spark in the spark plugs. The secondary, which consists of many thousands of turns of fine wire, is wound around the primary. The two coils act like a step-up transformer. The breaker points are electrical contacts in the circuit containing the primary. They are used to interrupt the current in the primary, causing an extremely short, high-voltage burst of current in the secondary. This current is directed to the spark plugs.

Magneto ignition was developed in 1878 by Nikolaus August Otto. It was widely used on early automobiles.

http://science.howstuffworks.com/magneto-info.htm

Carburetor

Carburetor Theory

The carburetor has one main function: to regulate engine speed. It accomplishes this by adjusting the amount of air and fuel that reaches the engine chamber, which then sustains combustion.

For a low-speed idle you have a small amount of air and fuel entering the engine. This lowers the chemical mixture entering the combustion chamber, and thus lessens engine power and subsequently lowers the RPM (revolutions per minute). As we open the throttle, the carb allows more air and fuel into the combustion chamber, thus increasing engine power and RPM's.

The Venturi Effect

What allows the carb to pull fuel from the fuel tank is the Venturi effect, a phenomena related to the Bernoulli principle. This states the velocity of a fluid entering a tube increases as it passes through a smaller diameter region.

Fluids are generally incompressible, so the same amount of fluid (volume) is going to try to get through a volumetric cross-section of tube - if you make the diameter smaller, the fluid has to move faster to get through.

In a carburetor, this increase in air speed allows more fuel to be drawn from the float chamber (a fuel reservoir) through the jet, where it is somewhat atomized.

This low pressure region is precisely where fuel enters the carburetor throat. This is what allows the engine to "suck" fuel from the gas tank.

Moped repair manual

For the Puch and pocket-bike groups - you may find some good repair ideas here:


http://blizzard.rwic.und.edu/~nordlie/moped/repair.html