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Why Is the Riding Lawn Mower Backfiring?

The loud boom of lawn mower backfiring can annoy or frighten. It also usually has a really simple cause that the riding lawn mower owner can easily fix.

The most common causes of backfiring include:

  • lowering the engine's speed too quickly,
  • using gasoline containing high alcohol blends,
  • a too lean carburetor adjustment,
  • poor muffler construction induces backfiring,
  • higher than normal engine temperatures,
  • sensitive carburetors induce backfire due to their internal transitional passages which cannot be corrected.

The jury is out on how much damage backfires due to the riding lawn mower engine. It does present a danger to the user. Be careful and take additional safety precautions if the consumer tries to fix the riding lawn mower them self.

Backfire Defined

The term backfire refers to a popping noise caused when gasoline ignites outside of the engine's combustion chamber. Rapid deceleration can cause a backfire. The mower's engine attempts to bring engine timing in line with the lower throttle. This puts excess air in the mix which creates a lean blend. That blend goes into the exhaust system because of incomplete combustion from mistiming. When it spontaneously combusts the backfire sound is heard.

Avoiding Backfires

A few simple tasks can ensure the riding lawn mower does not backfire. Some refer to operator control, others to riding lawn mower maintenance.

  • Learn to decelerate gradually. A smooth transition reduces or eliminates backfires.
  • Adjust the mower's carburetor to suit a richer gas mix. Have a professional do this.
  • Use gas that's a no-alcohol blend.
  • Increase airflow over the engine to cool it. This requires modifying the riding lawn mower. Another option is to stop the mower periodically to let it rest.
  • Replace the muffler. Poor construction or wear and tear can cause problems.
  • Water entering the fuel mix causes power loss and backfires. Empty the gasoline. Properly dispose of it. Add fresh gasoline.
  • Replace a worn or old spark plug. An improperly functioning spark plug creates a weak spark resulting in gas igniting, not in the cylinder, but in the muffler.

riding lawn mower backfiringThe problem could be as simple as a spark plug. Damage, wear or the incorrect gap between electrodes can create too weak a spark. This causes the fuel to ignite when it reaches the muffler rather than in the cylinder as it should. This produces a loud backfire. That’s a sign to check the spark plug first – the loudness. If the plug tests well, move on to check the ignition coil. If it tests well, check the engine’s timing.

Although sticky valves might sound like a tasty appetizer dish, you don’t want them. A small engine’s firing chamber, also called the cylinder, has valves sealing it. In precise timing, one valve opens letting gas and air mix into the cylinder while another opens to let the exhaust gases exit after combustion.

The engine backfires and responds sluggishly providing poor power if the valves remain open too long. The extended open time lets raw gas pass over to the muffler. Contact a professional mechanic to repair this issue since it involves taking apart the engine.

Sticky valves present a rather frequent issue and so do spark plug problems. For this reason, both items represent part of the annual recommended tune-up for a small engine. It’s normal for timing between the valves and engine to de-regulate. A tune-up consists of changing the fuel filter and spark plug and cleaning the wires and plug chamber.

Low fuel pressure can cause backfires, too. The two main issues leading to low fuel pressure are old fuel filters and fuel pump failure.

Lawn Mower engine and fuel lineWith respect to an afterlife, five main causes exist. If the user shuts off the engine at a high RPM, it causes gas to flow through the engine. As with backfire, the gas containing alcohol ignites more easily. Mufflers can be the culprit with an afterlife, too. Some small engine mufflers feature poor design or manufacturing practices. A simple carburetor adjustment could correct the issue. Finally, the solenoid that handles anti-after fire may be malfunctioning.

Take time before each use to examine the carburetor, engine and fuel line for holes and gaps in the metal parts. Look for metal fatigue, rust and severe impact damage. Holes in these areas let in extra air which reduces engine combustion. In the fuel line, look for cuts, gashes or holes. Also, examine the area where attaches to the carburetor and engine. Damage of this type lets extra air into the gas and the motor. Replace any parts that have sustained damage.

Disclosure: Some of the links in this post are 'affiliate links.' This means if you click on the link and purchase the item, I will receive an affiliate commission.
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