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How to Tune Small 4 Cycle Gasoline Engines

By Shirley Porras

It is very important to keep your small 4 cycle engine well tuned by performing a yearly tuneup. Four-stroke engines run better when you burn a higher octane premium gas. A well-tuned carburetor is key to keeping your engine running smoothly. Before storing your lawn equipment for the winter, it is a good idea to pour a gas stabilizer in your gas tank to prevent any buildup in the fuel system.

Purchase the tuneup kit that best suits your engine. Two different tuneup kits are made for the bigger 4 stroke engines: the single cylinder head engine with one spark plug, and the twin cylinder head with two spark plugs.

Remove the spark plug wires from the spark plugs. Remove the old spark plugs and replace with new ones. Inspect the spark plug wires for wear and cuts before putting them back on. If they do have wear and cuts, replace them. Remove the flywheel fan cover shroud located on top of the block for both engines. The flywheel is bolted to the crankshaft. Remove the nut holding the flywheel in place and pull the flywheel completely off.

Replace the points and condenser behind the flywheel with new ones. Adjust points to factory recommendations per your repair manual. Place the flywheel back on the crankshaft. Screw the nut back on the end of crankshaft and tighten it. Replace the fan cover shroud back on and bolt it on tight.

Remove the air cleaner off the carburetor. Locate your carburetor air fuel mixture screw. It will be either on the front or to the side of the carburetor, depending on your model. Turn the air mixture screw clockwise all the way in while the engine is off, then turn counterclockwise one and three-quarter turns for accurate setting.

Turn your engine back on. Locate the idle screw located on the side of your carburetor mounted to the gas throttle assembly. While the engine is running, turn the screw clockwise to raise the idle RPM of your engine. Turn counterclockwise to slow your engine RPM down. Remove the old filter foam off the air cleaner housing and replace it with a new one.


Things You Will Need

  • Set of open-end wrenches
  • Screwdrivers
  • Pliers
  • Spark plug wrench
  • Ratchet
  • Spark plugs
  • Ignition points
  • Gear pulley
  • Feeler gauge
  • Repair manual
  • Air cleaner foam


About the Author


Shirley Porras was trained as an alcohol and drug counselor at the University of California in Northern California. She routinely writes treatment plans and program schematics in her field and credits a combined package of knowledge, dedication, passion and humor for her success.