We’re all used to hearing about backfires, but quite often what we are hearing is an afterfire. There are a number of differences between the two, in what causes them and how to fix them. So how can we recognize the difference between the two? Once we recognize the difference, how can we diagnose the cause of an afterfire and fix it?
What is an afterfire?
An afterfire is a popping sound or a bang that occurs after the mower has been turned off.
What is the difference between an afterfire and a backfire?
An afterfire is essentially a type of backfire – not all backfires are afterfires, but all afterfires are backfire. An afterfire only occurs after the engine has been shut down, while a backfire can occur at any time.
Causes of afterfire, and how to fix them.
Afterfires have the same primary cause as backfires – ignition of the fuel-air mixture in the muffler. Shutting an engine off at high RPMs can allow for some of the mixture to be pumped through on to a hot muffler, causing an afterfire. To avoid this, bring the revs of the engine down gradually for 15-20 seconds before a complete shut-off.
A high-alcohol fuel can also lead to an afterfire, as it ignites easily and produces a hotter engine and muffler, meaning that your mix will be more sensitive to heat while simultaneously making the engine hotter. This is a dangerous combination that, as talked about before, can be unhealthy for your lawn mower.
Check your carburetor for a proper mix, and make sure the engine is being cooled properly – if you’re experiencing afterfires and backfires both, this is probably where you will find the problem, as these are common causes of both.
Many companies have recognized that afterfires happen, but are undesirable. Many newer mowers now come equipped with anti-afterfire solenoids to prevent these incidents. If your mower is equipped with one, make sure it is installed properly and functioning properly. Also, make sure you are shutting down the engine per manufacturers instructions – some anti-afterfire solenoids will not prevent afterfires when shutting off at low RPMs, even though this is counter-intuitive.
Now that you know the difference between an afterfire and a backfire, and how to fix them, you can go back to mowing without worrying about giving your elderly neighbor a heart attack when your mower backfires at random times. Your neighbors will thank you as well – there’s little worse than a backfiring lawn mower when they’re trying to catch an afternoon nap.