Tag: lawn mower engine backfires

Lawn Mower Repair Tips

Fire Comes Out of Air Filter Box on Lawn Mower

Anytime you have a fire on an engine it is a safety problem due to the gasoline tank on the machine. A fire is not easily extinguished if the gas tank ignites and could catch other things on fire around the lawn mower.

With that being said, it is finding out why it is backfiring that is the most important part of this problem. In order for a backfire to occur through the air filter box, the intake valve must be open while the spark plug is igniting the mixture. The intake valve could have some carbon buildup under the valve seat or it could be hanging open because the valve guide is causing it to stick.

Another possibility is that the ignition timing is not correct. If the lawn mower blade has contacted something such as a root and this is a push mower, the flywheel key may be partially sheared and cause the timing to be incorrect. It is also possible that the timing gear has damage to it.

All of these items should be checked out to determine which is causing the problem and eliminate them one by one.

Lawn Mower Repair Tips, Outdoor Power Equipment Reviews, Push and Self-Propelled Lawn Mower Repair, Riding Lawn Mower Repair, Zero Turn Lawn Mower Repair

My Lawnmower Makes a Big Bang or Backfire While Mowing

You are just mowing along and your engine suddenly backfires and then it starts to continue running like normal. What could be causing this and how do I resolve it?

An engine backfire can be caused by an electrical problem or a mechanical one. In most cases it can be tracked down to an electrical problem, more specifically in the ignition system. If the ignition coil becomes too hot or has an internal breakdown, the spark will become intermittent and the combustion chamber can be ignited at the wrong time and cause a backfire out of the intake or exhaust.

The ignition kill wire could also have been compromised and partially broken because of rodent damage or heat and vibration. So you want to check it and is usually a black or gray wire that is attached to the ignition coil.

There could also be a problem with the ignition switch.

If the ignition system is working normally, then the search begins on the mechanical portion of the engine. A leak down test will need to be performed initially to determine if the intake or the exhaust valve is leaking. If one of them is leaking, the burning gasses will pass through them and cause a backfire while the engine is running and particularly under a load such as cutting the grass.

If you need a lawn mower repair shop near you to fix your mower, visit our Locations page for assistance.

Lawn Mower Repair Tips, Outdoor Power Equipment Reviews, Push and Self-Propelled Lawn Mower Repair, Riding Lawn Mower Repair, Zero Turn Lawn Mower Repair

My Lawn Mower Backfires and Then Dies

The first thing you must find out is if it backfires through the exhaust or the intake or carburetor side of the engine. In a lot of cases it will be on the intake side of the engine. When it backfires, it is sending out raw fuel out the carburetor and the ignition is igniting it and you may see flames come through the air filter or it blows off the air filter box completely. When it blows the fuel out, the combustion chamber has no fuel left in or very little and the engine dies. The same thing can happen in the exhaust.

So obviously we have a timing problem or a valve problem. A set of tests must be done to determine what the problem is. The first test is a leak down test. This will tell you if your valves are leaking and which one is the culprit. It could be both of them causing the problem.

Checking the engines timing is more difficult and requires that the engine be taken apart to see if the timing gear cam or chain has jumped a tooth. But before you go ripping things apart, check the flywheel key to make sure that it is not partially sheered. One some models you have to remove the flywheel to check it, but on most you remove the nut holding it in place and you will see it.

These tests are often out of reach for many home owners because they do not have the test equipment. Check our Locations page for a shop near you for help.