Pistons

Causes of Burned Pistons: The two basic causes of burned pistons in two-cycle engines are overheating or detonation in the cylinder.  The cylinders are cooled by air from the fan and equally by gasoline from the carburetor entering the cylinders.  Anything which reduces the effectiveness of these cooling systems can cause the pistons to burn.   If the engine fan is not working properly the cooling of the cylinders is reduced.   You should check the fan drive belt and adjust it if necessary.

The gasoline to air mixture is a vital factor in keeping the pistons cool.  Therefor the following problems can cause overheating:

Carburetor jets are too small; Air leak in fuel hoses, filter or primer bulb between tank and carburetor; Leaking cylinder head gasket or base gasket allowing air to be drawn into the crankcase or cylinder and diluting the mixture; Leaking intake or exhaust gaskets; Spark plugs not correctly tightened.

Detonation is caused by any of the following:

Poor quality gasoline; Incorrect spark plugs or incorrect gap in spark plugs; Ignition timing too far advanced; Carbon deposits in cylinders.

Preventing Burned Pistons:

1. Check the color of the spark plug electrodes.

   Black or wet electrodes means mixture is too rich (too much gasoline - poor performance); White or gray means mixture is too lean (too little gasoline - danger of burning piston; Brown - good combustion.

2. Use cylinder head temperature gauges - temperature should not exceed 425 degrees F (218 degrees C);
   
3. Use exhaust gas temperature gauges - temperature should not exceed 1,245 degrees F (675 degrees C).