Lawn Mower: Engine Lacks Power

The air filter removes dirt and debris from the air entering the engine. Without the air filter, dirt and debris would plug the tiny fuel openings in the carburetor and allow dirt to cause costly damage to the piston and cylinder. It is a critical part in keeping the engine running properly. The air filter should be checked often and replaced as needed. If the air filter is neglected, the debris will build up on it until the required amount of air need for combustion can no longer pass through. When this occurs the engine may seem like it is lacking power. Other symptoms will be hard starting, the engine killing (especially under load), and black smoke from the exhaust. Servicing an air filter is easy to do and should be part of your lawnmower’s periodic maintenance. The filter should be inspected several times each mowing season and replaced at least once. It should be replaced more often if you mow in dusty conditions such as a sparse lawn or areas of weeds. The air filter will be located beneath the air filter cover. The cover is typically held in place by knobs, screws, or tabs. Remove the cover to expose the air filter. Carefully remove any grass or excessive debris built up on the filter before removing it from the air filter base. You want to make sure you don’t spill any of the debris into the carburetor intake. Once removed, the filter can be replaced or cleaned. Pleated paper or cloth filters should be replaced. Foam filters can be cleaned using dishwashing soap and water. When a foam filter begins to crumble, it should be replaced. Most foam filters will need to have a small amount of oil added to them to filter properly. Refer to your engines owner’s manual for specific instructions. To oil a foam filter, place it in a plastic bag and add a small amount of oil. Work the oil evenly into the filter with your fingers. Remove the filter from the bag and use a rag or paper towel to blot away the excess oil. Install your new or cleaned air filter back into the air filter base and reinstall the air filter cover. When replacing the air filter it is important to always use the exact filter called for by the manufacturer. The incorrect filter may not fit and seal properly. This will allow dirt and debris into the engine. Servicing your air filter often will keep your engine running great and help it to last for many years.

If your lawnmower engine seems to be lacking power, you might have piston and cylinder problems. The piston and cylinder work together to create power. After combustion, the piston is pushed down in the cylinder, which rotates the crankshaft. The power from the crankshaft drives both the blade and the mower’s drive wheels. Compression is created in the cylinder when combustion takes place. This compression is contained in the cylinder by the piston rings. The rings attach to the piston and seat against the cylinder walls. A thin film of oil, only a few molecules thick, keeps the rings from rubbing against the cylinder. As the rings wear, or if the rings and cylinder are damaged, compression will be lost. The lower the compression becomes the less power the engine will be able to generate. Once compression becomes low enough, the engine will no longer start. The piston rings and the cylinder will wear during normal engine use. A properly maintained lawnmower engine can easily provide decades of use with no compression-related issues. Most compression issues are the result of a lack of maintenance. It is important to maintain the air filter and perform regular oil changes. The most common issue that leads to a loss of compression is dust entering the engine caused by a missing or damaged air filter. Using the wrong air filter can also allow dust into the engine as the wrong filter often doesn’t seal correctly. Once dust enters the engine it mixes with the engine oil and acts like sandpaper. The dust will quickly wear the piston rings and the cylinder walls. Another common problem that will lead to a lack of compression is insufficient lubrication. The piston rings are separated from the cylinder wall by just a few molecules of engine oil. If oil isn’t present, the rings will contact the cylinder, causing heat and wear almost immediately. Low oil will often cause metal to transfer between the rings and the cylinder. This will create grooves in the cylinder wall called galling. Damage from insufficient lubrication occurs very quickly. Running an engine for just a couple of minutes without oil can be all it takes to damage it to the point that it no longer has enough compression to start. You can test your engine for low compression using a compression gauge. Compression gauges are available from most auto parts stores. You will need the manufacturers specs for the correct compression for your engine. Fixing an engine with low compression is not an easy repair. Because the piston rings and the cylinder work together to create compression, both will usually need to be replaced when there is a compression issue. Depending on the severity of the damage, the piston will often need to be replaced as well. The repair will require special tools and a complete tear-down of the engine. This is a repair you might want to take to a small engine repair shop unless you have experience doing advanced small engine repairs.