Motorcycle Backfire: Causes & Fixes

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A backfire describes the loud pop or bang you hear in your motorcycle’s exhaust when it’s not tuned quite right.

There are a number of different reasons why your motorcycle backfires, some easier to fix than others.

What Causes a Motorcycle to Backfire?

Backfire is caused by a secondary, unexpected combustion when there is unburnt fuel in the exhaust.

The underlying cause of motorcycle backfires is an improper fuel mixture.

Reasons for Motorcycle Backfire

The improper fuel mixture that causes the backfire can be attributed to a number of things. The most common ones to check are:

  • Loose exhaust pipes or carb manifolds.
  • Improper exhaust system for the current jetting.
  • Weak spark.
  • Improper ignition timing.
  • Too much fuel.
  • Too much air.
  • Dirty carbs or clogged jets.

Motorcycle Backfire on Acceleration

If your motorcycle backfires when your speed up, the likely culprits include:

  • The intake circuit.
  • Ignition timing.
  • Carbs out of sync.
  • Improper valve clearance.

When you accelerate and twist the throttle, you introduce more air to the air fuel mixture, if there is a leak or timing is off, the mixture will be incorrect and a backfire can happen.

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If your motorcycle is backfiring on acceleration, start with the items above.

Motorcycle Backfire on Deceleration

The most common causes for backfiring as you slow down and close the throttle, include:

  • Aftermarket or open exhausts without carb jetting.
  • Carbs out of sync.
  • Low compression.

Any of these situations can cause excess fuel left in the exhaust, which eventually heats up, ignites, and “pops.”

Fixing a Motorcycle Backfire

Start with the easy fixes first and move down the list:

Backfire can be prevented and a properly tuned engine can be maintained with regular maintenance and inspection.

If you get a backfire every once in a while, it’s probably not much to worry about.

However, if your motorcycle is constantly backfiring, you’ll want to identify and fix the cause of the issue.

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