3 Steps to Better Mower Engine Performance

Tips from Kohler Engines on gas cans, filters and engine oil.

Commercial mowers are rather complex machines. It's important to keep your mower, engine and drive system operator's manuals readily accessible so you can quickly reference service needs and recommendations in order to get the best possible performance out of your mower.

The engine is a logical place to start. Scott Mack, senior training specialist at Kohler Engines, offers some insights into why a mower sometimes doesn't perform as well as a contractor would like it to.

1. Unsealed gas can. "Very often I see a gas can with a tethered cap hanging loose," Mack relates. This allows air and moisture into the gas can. "With today's ethanol fuels (which absorb water at a much higher rate than traditional gasoline), this is a mistake no different than intentionally pouring a cup of water into your gas tank."

Additionally, leaving a gas can open allows light end fuel vapors to escape. "If you have ever seen a sealed gas can expand when sitting in the sun, you can imagine how much air wants to escape," Mack explains. "When you remove the cap and let the air out, you are also releasing many of the fuel's light ends. This is the vapor part of the mixture that helps the engine start easier. When the can cools down in the evening shade, that same amount of condensed air will again enter the unsealed can. With the air comes moisture. Ethanol attracts moisture and mixes it into the fuel. When too much moisture is absorbed, phase separation takes place. You end up with the bond of ethanol and water that drops to the bottom of the can, leaving unwanted gas on top."

So what's the problem, you ask? That mixture at the bottom of the can is the first fuel delivered to the carburetor. So the engine will probably be harder to get started. And even if it starts, the engine won't run as well. "Furthermore, that fuel at the bottom of the can is a corrosive mixture that will cause damage to the carburetor," Mack adds.

2. Forgetting the filters. Filters are a big deal, so change them regularly. Most people will change the oil filter during an oil change. But don’t stop there, Mack advises.

The air filter should be changed when dirty. "Paper elements should not be cleaned," Mack points out. "Foam pre-cleaners can be cleaned with detergent and water, but solvents and fuels often will deteriorate the foam. Check your owner's manual to see if oil should be applied to the pre-cleaner."

If you do opt to simply clean your existing air filter, never use compressed air. This will cause damage that you may not see while also allowing dirt into the engine. "A light tap is all I would suggest," Mack says.

The fuel filter is usually the most neglected service item, according to Mack. Some people never change it at all; they don't think there's a problem because they can't see what's lurking at the bottom of their mower's fuel tank because it's dark down there. "But take a look into your gas can to see what is floating along the bottom," Mack recommends. "That is what's being delivered into your engine. If dirt enters the carburetor, you will often find fuel leaking, as the needle and seat cannot stop the fuel from entering."

3. Check that oil. Before each mowing, check the oil level. This only takes a few seconds and will tell you if the engine is beginning to consume oil while also reminding you that the next change may be coming soon. "Oil consumption can be as bad to repair as the cost of a short block replacement or as simple and inexpensive as a breather component," Mack points out. "Your dealer can diagnose the problem for you."

Other than that, simply change the oil according to your owner’s manual. The manual will tell you what kind of oil is best to use and at what intervals.