How to Tune Up Your Gas-Powered Lawn Mower

Inspecting the Points and Condenser

Once you remove the flywheel, you'll see a cover with wires protruding from it. Remove the screws to gain access to the points and condenser.

Turn the crankshaft by hand until the points and the condenser move as wide apart as possible. Now look at the flat spots on the condenser and the points and inspect them for burn marks or carbon build-up.

If the burn marks are light, you can clean them off by using fine-grit sandpaper. Place a small piece between the points and condenser and turn the crankshaft until they close on the sandpaper. Lightly slide the sandpaper back and forth a few times, and then turn the crankshaft again to open the gap. Repeat this step to clean the face of the points, then insert a dollar bill between the points and condenser and turn the crankshaft until they close. Move the dollar bill back and forth to remove any grit.

Check the gap with a feeler gauge with the points opened to their widest point. You may need to turn the crankshaft back and forth to achieve this. Slide a .030 feeler gauge between the flat spots on the points and condenser. They are gapped properly when you feel a slight resistance when you slide the gauge in without moving the points. If the gauge is too loose or too tight, you'll need to adjust the gap.

To adjust the gap, loosen the screw that holds the condenser in place and slide it until the proper gap is achieved without causing the points to move. Then, tighten the screw on the condenser. Check the gap once more for proper adjustment. Repeat this step if necessary.

Insert a dollar bill between the points and condenser and close the points. Slide the dollar bill back and forth. This will remove any oils from the face of the points and condenser that could cause them to fail.

Replacing the Points and Condenser

If the points and condenser can't be cleaned, you'll need to replace them. Start by removing the screw from the long spacer that holds the points in place. Remove the spring from the points and lift them from the tray.

Find the spring compressor in the tune-up kit. This tool fits over the end of the condenser and allows you to compress the spring and remove the wires that are part of the ignition system. Pull the wires from the condenser and remove the spring compressor and spring. Loosen the screw and remove the condenser.

Once the points and condenser are removed, inspect the tray and remove any oil and dirt that may have accumulated.

Install the new points and condenser by reversing the procedure for removing them. Follow the instructions that came with the tune-up kit if necessary.

Check the gap with a feeler gauge and set it to .030 by sliding the condenser back and forth until the proper gap is set. Check all components for proper placement, then replace the cover and screws.

Slide the flywheel back onto the crankshaft and align the groove in the flywheel with the groove in the crankshaft. Find the new shear pin that came with your tune-up kit. (Note: The curved side fits into the groove in the crankshaft and the flat side fits into the groove in the flywheel.)

Slide the convex washer over the crankshaft and replace the starter clutch and tighten, then reinstall the blower housing and replace the bolts.

Removing, Inspecting, and Replacing the Spark Plug

Use a spark plug wrench to remove the spark plug. Once it's removed, inspect the electrode (the round wire that protrudes from the bottom of the spark plug) for signs of wear. If the electrode appears burnt or worn, you will need to replace it. The proper gap for a spark plug is between .025 and .030. Checking the gap on the old plug is another way of checking for wear. If the gauge slides freely in this gap, it will need to be replaced

If the spark plug needs to be replaced, you must replace it with one of the same size. Check the numbers on the spark plug and replace it with one that has the same numbers or one from another company that is a direct replacement for your plug.

Gap the new plug to the gap that's marked on the package and replace the plug in the head, taking care not to over-tighten. Don't replace the spark plug wire at this time.

Cleaning and Replacing the Air Filter

The air filter is located under the cover that's on top of the carburetor. Remove the screw in the center and take off the cover. Pull the filter from the housing and inspect it for dirt and oil. Clean the filter in a mild soap and water solution. Squeeze the excess water from the filter and allow it to dry completely. Clean the housing with soap and water or degreaser before replacing the filter. If the filter appears torn or extremely dirty, replace it with a new filter.

While you have the filter removed, check to make sure the opening to the carburetor is free from dirt and oil. Use a clean, lint-free cloth to remove any dirt from the opening.

Add a few drops of motor oil to the filter and return it to the housing. Replace the cover and screw the housing back onto the carburetor.

Setting the Air/Fuel Mixture

The needle valve is used to properly set the fuel/air mixture on the carburetor. The needle valve is located on the carburetor. It has a slot in it for a screwdriver to be inserted.

Insert a screwdriver and turn the needle valve clockwise until it stops. Count the number of full and partial turns needed to close the valve all the way. Write this number down as a reference in case you need to set the valve back to the original setting. Now screw the needle valve out counter-clockwise 2-1/2 turns. This is the proper starting point for the air/fuel mixture.

TESTING THE ENGINE FOR PROPER OPERATION

Replace the spark plug wire and set the throttle control to choke. Pull the cord or starter until the engine starts. If it takes more than two or three pulls for the engine to fire and run, go over these instructions once more to see if you missed a step and recheck the spark plug and points gap, if necessary.

Once the engine is running, pull the throttle control back to idle. The engine should be running smoothly. If the engine sounds rough or stalls, adjust the needle valve by ¼-turn increments and restart the engine. Depending on the age and condition of the engine, you may need to adjust the needle valve several times to find the proper mixture.

Adjust the throttle from idle to full power several times, checking for smooth operation of the engine. Adjust the needle valve as necessary for proper operation through all throttle ranges.

CONCLUSION

This article was written to give you the basic information needed to properly tune up your small engine. After you perform the tune-up steps explained here, your small engine will be running at peak efficiency. You can obtain more detailed information on small-engine repair by visiting the Web sites that follow and by checking out one or more of the books listed below.

Home 1 2 3 4