Lawn Mower Storage Mistakes That Cost You a Spring Repair Bill

Every spring there's a rush at small engine repair shops of people with mowers that won't start. Almost every one of those mowers sat in the garage for winter with old fuel in the carburetor. The repair isn't complicated — the carburetor gets cleaned or replaced — but it costs time and money that was entirely preventable the previous October.

The gas tank problem

Old gasoline is the number-one killer of small engines in storage. Gasoline, especially E10 ethanol blends, degrades within thirty to sixty days. The ethanol attracts moisture, separates from the gasoline, and the residue left behind varnishes the carburetor's tiny fuel passages. When you try to start the mower in spring, the fuel can't flow properly and the engine either won't start or runs rough and dies.

The solution is one of two things: add a quality fuel stabilizer to the tank at the last mow of the season, run the engine for a few minutes to circulate it through the carb, and store with a full tank. Or drain the tank completely and run the engine until it stops on its own, which clears fuel from the carb float bowl. The second approach is more thorough but leaves internal metal surfaces exposed. Either method is fine; just pick one and do it.

Oil change logistics

Used small engine oil has combustion acids in it that corrode engine internals during storage. Changing the oil before you put the mower away — rather than in spring — costs the same and gives better protection. The only annoying part is disposing of the old oil: don't pour it down the drain. Auto parts stores and many municipal waste facilities take used oil at no charge.

The spark plug is the other piece. If the mower's been running for two or more seasons, pull the plug and look at it. A heavily fouled or gap-worn spark plug will cause the hard-start problem you blame on the carburetor. They cost a few dollars and take two minutes to swap.

The underside that nobody cleans

Grass clippings packed under the deck hold moisture, which accelerates corrosion of the deck and blade mounting hardware. Disconnecting the spark plug wire before reaching under the deck is the safety step everyone skips and shouldn't. Scrape the underside clean, hose if needed, and dry before storage. Apply a thin coat of rust-inhibiting spray or used oil to the underside of the deck to prevent surface rust from bonding to the steel.

Blade sharpening during fall storage is smarter than waiting for spring: you can take your time, the blade is cool, and you'll be ready to mow the moment the grass starts growing. A blade sharpening kit with a guide makes the job straightforward even for a first-timer. Reconnect the spark plug only after everything is stored properly.

What I'd skip

Skip the mothball-in-the-storage-area advice. Mothballs have naphthalene or paradichlorobenzene vapors that can contaminate fuel and are genuinely unpleasant to work around in spring. A sealed bucket of steel wool stuffed near entry gaps accomplishes the rodent deterrence without the chemical problem.

Also skip storing the mower next to a water heater or furnace if you can avoid it. The temperature cycling near combustion appliances accelerates fuel degradation in any residual gas you didn't fully drain. A corner of the garage away from heat sources and off the concrete floor (a pallet works) is the right storage spot. Thirty minutes of fall prep means the first mow of spring isn't a diagnostic exercise.