Fuel Supply

• The fuel system is a frequent cause of problems because there are many places for things to go wrong. The place to start your diagnosis is by checking to see if fuel is going to the cylinder. This can be done by removing the spark plug and seeing if it is wet after you have tried to start the engine. If it is not wet, you need to check the fuel system. Look for a disconnected hose or a fuel leak. Remove the fuel filter from the fuel tank and examine the hose and filter for damage or clogging. Empty and flush the fuel tank and fill it with new fuel/oil mix.
  
  

Exhaust System

• Exhaust system problems are common with two-cycle engines because they need to have low back pressure. Diagnosing the problem begins with listening to the engine. If it sounds like it is “stopped up,” it may well be. Check the exhaust screen or exhaust port to see if they are partially blocked by a buildup of carbon.
  
  

Air Intake/Carburetor

• Excessive carbon build-up results from problems with the fuel/air ratio. It is the function of the air intake/carburetor to maintain the proper airflow to mix with the fuel. Check the intake air filter. If your engine has an impulse hose running from the base of the cylinder to the carburetor, check it for leaks.
  
  If your engine does not run well at idle or has a poor response to the throttle, this indicates your idle adjustment is set too lean. If the engine runs too fast or over speeds, this can indicate a too-lean run adjustment. The run adjustment controls the speed and power available from the engine. The main idle adjustment is used to control the idle speed after the other two are set. These adjustments should be changed carefully as engine damage is possible. If these checks of the fuel and air systems have not located the problem, it may be that the fuel screen in the carburetor is clogged or the fuel-pump diaphragm has stiffened with age or the carburetor needs cleaning and rebuilding.
  
  

Ignition

• The problem can be in the ignition if the engine does not start. The first place to start is to inspect the spark plug wire, then to check the spark plug. If the gap between the flywheel and the ignition coil is not the right distance, this can cause poor spark plug operation as indicated by hard starting or less-than-normal power.
  
  

Compression

• The two-cycle engine must have adequate compression in the cylinder head and in the crankcase. Loss of power is caused by low compression in the cylinder head as the result of damage to the cylinder. This damage can be found by examining the cylinder through the exhaust port for scratching and other damage. Compression itself can be measured using a compression gauge. The minimum pressure should be over 100 pounds per square inch.
  
  Crankcase compression drives the diaphragm in the carburetor that supplies the fuel/oil mixture to the engine. Low pressure will result in loss of engine power. The leaks may be caused by faulty gaskets or seals at the joining of the crankcase halves, at the base of the cylinder or at the crankshaft. The leaks can be found by looking for oil at these locations.