How to Clean a Gas Tank On a Lawn Mower

If your lawnmower sits unused for a prolonged period, it may fail to fire up when you're in the mood to spruce up the yard. Often, this happens because the gas degraded over time. It could also happen because debris or condensation is in the tank and has clogged the fuel line.

Pouring gasoline into lawn mower
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How to Clean a Gas Tank on a Lawn Mower

Before you panic that the mower is on the fritz and its end is nigh, it's time to drain and clean the fuel tank as that could solve all your issues.

Safety First

Working with open fuel sources and gasoline is always a fire hazard. Make sure you're being fire smart by not smoking in the vicinity.

Remove the Spark Plug

This is just another safety precaution – in case, by some bizarre fluke, lingering vapors are enough to get the engine to start and cause the blade to spin while you're working on things. Never work on your mower with the spark plug attached.

This is also a chance to check the plug to see if maybe a new one is warranted. New spark plugs are cheap and can make a huge difference in performance.

Drain the Tank

Have an approved gas caddy ready before you get cracking. Now, squeeze the clamp that attaches the fuel line to the carburetor and take the tube off. Next, remove the clamp and line from the base of the gas tank.

Put the gas caddy under the tank and drain the gas out. Set it aside for now.

Clean the Carburetor and Tank

Take a canister of carburetor cleaner and carefully spray it into the intake hole where fuel enters the carburetor. Use the cleaner to spray into the outtake hole for the fuel line on the gas tank, and also spray thoroughly inside the tank.

Rinse the Tank

Don't use water to rinse your gas tank. Water residue can be a problem for fuel injectors and carburetors. Instead, rinse the tank out by adding a cup of fresh gas to the tank. Close it up and agitate the lawnmower so the gas sloshes around to fully rinse the tank. Drain this into the old gas you have in the fuel caddy.

This spent gas can't be reused in other working engines lest it clogs or damages them. Instead, perform a web search to find a fuel recycling station near you, and they'll take it off your hands.

Fill ‘Er Up

It's important to know that gas is only considered "fresh" for a couple weeks. Anything older than a month could have already begun degrading. So, don't proceed with filling the tank unless your gas is newly bought from a busy gas station.

With that said, and the tank now clean, reattach the fuel line to the carburetor and then to the gas tank. Add fresh fuel to the tank. Put the spark plug back in place.

Now, start your engine. Ideally, it'll roar to life. If it doesn't, your problems may lie elsewhere. Cleaning or replacing the air filter might be the next step.

An Ounce of Prevention

In the future, buy gas in smaller quantities to ensure you're always using good-quality gas in your lawnmower. The longer gas sits, the more it degrades. Buy just enough to last two to four weeks. If you're going to let your mower sit while taking an extended vacation, consider adding fuel stabilizer to keep things healthy.

Better yet, throw open the throttle while mowing so you use all the fuel up before putting it in the shed. Doing this every month or so will ensure you never let the gas get stale in your tank. Stale gas degrades rubber lines and causes the inside of your tank to rust, generating debris that damages carburetors and other engine parts.

Being gas-conscious will extend the life of your engine.