How to Troubleshoot Small Air Cooled Engines

Starting Problems

• 1

  Check that the engine has a supply of fuel by:

  1. Ensuring that the fuel shutoff valve is open,

  2. Filling the fuel tank,

  3. Ensuring that the vent hole in the fuel tank filler cap is not plugged, and

  4. Removing the spark plug (using a spark-plug socket wrench) and smelling for fuel in the cylinder.

  Correct any evident problems. If fuel is still not flowing, check for water or "gunk" in the fuel tank or for a blocked fuel line.

• 2

  Remove the spark plug and inspect the contacts. Clean the contacts if they are dirty and regap the plug using a feeler gauge. Replace the spark plug if the contacts are eroded.

  Hold the ignition lead with insulated pliers. Crank the engine while holding the ignition lead close to a metal ground on the engine. Reinstall the ignition lead and check for good contact between the lead and the spark-plug connector. Lack of a spark will require repair of the ignition system.

• 3

  Remove the air filter cover. Clean the air filter or replace it if necessary.

  Remove the air filter housing and check the carburetor for dirt and debris. Blockage of the carburetor will require a carburetor overhaul. Carburetor adjustment can be done if you have the skills.

  Crank the engine to see if air is drawn into the carburetor. Lack of air flow indicates an internal engine malfunction requiring significant repair.

Running Problems

• 4

  Observe how the engine runs at various speeds and loads. Loss of power at high speeds or loads indicates a problem with fuel flow or the need for a carburetor or governor adjustment. Check the:

  1. Fuel tank filler cap vent, and clean if necessary.

  2. Fuel filter, and clean or replace if needed.

  3. Fuel line for blockage.

  Smoke from the engine indicates a too rich fuel/air mixture. This requires a carburetor adjustment or improving the airflow into the engine. Remove the air filter and check the engine air intake for blockage. Clean or replace the air filter if needed.

• 5

  If the engine runs "rough," clean and regap, or replace the spark plug. Also, check the spark-plug lead for solid contact at both ends and for breaks in the insulation. Other malfunctions can cause a rough-running engine and require repair, such as faulty breaker points, a weak valve spring or a loose flywheel.

• 6

  Clean the engine, particularly the cooling fins, if the engine overheats. Low oil level can also cause overheating. Get the engine repaired if it exhibits symptoms of improper fuel/air ratio such as "knocking" (which is caused by carbon deposits in the cylinder) or low power due to a leaky intake gasket.