How often does my Lawn mower need to be tuned up?

Every year about the middle of summer, my mower gets harder to start, and it doesn’t run as strong as it did earlier in the season. I tune it up every spring, and it always runs on fresh fuel. How long can a mower go between tuneups?

The tune-up interval for a typical small engine on a mower is about 50 hours or once a season, whichever comes first, but there are exceptions, according to manufacturers. “Machines used under heavy loads such as high ambient temperatures, dusty conditions or tall grass will require more frequent servicing,” says Dennis Blair, technical service department manager for MTD, a manufacturer of lawnmowers and outdoor power equipment.

My guess is that your mower’s malaise is being caused by the alcohol content of today’s fuel blends. The alcohol in the fuel oxidizes to form a tenacious varnish inside the carburetor, which attracts moisture that causes corrosion. When it’s not doing that, the alcohol stays busy damaging plastic fuel components.

You mention you use fresh fuel, but I’d strongly recommend you do several things to improve your fuel supply and storage. First, use gasoline that has an octane rating no lower than 87, with an alcohol content no higher than 10 percent (E10). Next, a good rule of thumb is to buy only enough fuel to last two weeks. Take some fuel additive to the gas station and pour it into your fuel container before you fill up. You might also consider prepackaged fuel such as SEF Small Engine Fuel. Although expensive compared with fuel from the pump ($5.50 to $7.50 per quart), it’s 94 octane and completely free of ethanol. It requires no additives.

Other problems can surface by midseason, especially in machines that have been worked hard. The air cleaner gets clogged with dirt; the blade dulls; and if you do your cutting in the early morning, when the grass is wet with dew, the underside of the mower deck gets plastered with a thick layer of grass clippings.

Here’s a midseason checklist to cover your mower’s service points:

1. Scrape the Deck. Disconnect the spark plug and siphon out the fuel tank or remove it, then tip the mower back and give the deck a thorough scraping with a putty knife and a wire brush.

2. Sharpen the Blade. Remove the blade and sharpen it with a mill bastard file. Take off an equal amount of metal from both sidesyou can check by balancing the blade on a bolt clamped in a bench vise or by using a store-bought blade balancer. Employ a torque wrench when you reinstall the blade; tighten the blade-retaining bolt according to the specs in the owner’s manual.

3. Check the Plug. Install a new, properly gapped plug after 100 hours of operation or once a season, whichever comes first.

4. Service the Air Filter. According to engine manufacturer Briggs & Stratton, paper or foam filters should be replaced every 25 hours of operation, while paper filters that have a foam filter precleaner last for 100 hours of operation. Never use compressed air to blow out a paper air cleaner, because you run the risk of perforating the paper. “A teaspoon of dust that makes its way past a hole in the air filter can destroy an engine,” according to Blair.

5. Clean the Flywheel. If your mower sees more than 4 hours of use a week or runs in dusty and dirty conditions, uncover the flywheel at midseason and brush off the fins with an old paintbrush.

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