What to Do When Your Lawn Mower Engine Is Backfiring

There are many reasons for a backfiring engine. Troubleshoot them one-by-one.

By Successful Farming Staff

A backfiring lawn mower can not only be annoying — it can be dangerous.

We’re answering a question from Dena in Mississippi. She said, “I have a 2002 John Deere riding lawn mower, and always try to take good care of it, but every time I shut it off, it backfires. It sounds like a gun going off, and my dogs tear out to the woods. It runs good and cuts good, but I am concerned about the backfiring.”

Shane Louwerens is the author of “A John Deere Fit for a King,” a novel he wrote about refurbishing Elvis Presley’s 1963 John Deere 4010 with four of his former students at Mississippi Northwest Community College. He said a backfiring engine is basically a little explosion that happens when the air and fuel mixture isn’t right.

“It’s the same thing as your engine firing, except it’s firing at the wrong time. If you were to be dumping too much fuel through a carburetor into your engine,” Louwerens said. “Then what happens is you’ve got too much fuel, it didn’t burn it all, then it ends up igniting at the wrong time, and then you get that backfire effect.”

Louwerens said there are many reasons this could happen, so you just have to go through each system to rule out potential causes. The problem might be faulty intake and exhaust valves, a clogged carburetor, or a misfiring spark plug.

Taking Caution
While you’re troubleshooting, Louwerens advises you to be careful, because he’s seen a lawn mower catch fire while it was being checked for backfiring. Fuel vapors trapped in the muffler will create a backfire.

“That’s the bad thing, when people are working on it, and they’re trying to figure this stuff out, you know when you’re draining the fuel bowl and you’re doing all this stuff, you’ve got to realize that it’s the vapors, the fumes of gasoline, the spark — that’s what’s going to start your fire,” Louwerens said. “So you’ve got safety issues there with that. And I have seen it cause damage to mufflers — I’ve seen it literally blow an end out of a muffler before.”

Louwerens said the occasional hiccup out of the engine probably isn’t a problem, but if it happens all the time, it should be looked at to prevent longterm damage.