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Frequently Asked Questions

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Backfire/Antifire from Carburetor or Muffler

What causes engine backfire out of the carburetor or muffler?

"Backfire" and "antifire" are conditions described as a loud bang, poof, explosion, etc., when idling the engine down or after the engine has been shut off.
Note: "Afterfire" and/or "Backfire" will not harm the engine at all!)

"Afterfire" occurs after the engine has been shut off.

Some possible causes include:

  • Shutting off the engine at high RPM. This can result in some fuel being pumped through the engine, and into the hot muffler, causing that fuel to ignite.

  • Gasoline that contains alcohol has a tendency to ignite easier and cause the engine to run slightly hotter. This, combined with a hot muffler, can cause afterfire.

  • The type of muffler that has been installed by the equipment manufacturer may cause afterfire.

  • Carburetor adjustments may not be properly set to insure correct engine performance.

  • If the anti-afterfire solenoid is installed it may not be working properly.

Some possible cures include:

  • Idling the engine down to the proper idle speed for 15-30 seconds. This would allow the engine to cool somewhat before shutting the engine down.

  • Changing to a different non-alcohol or alcohol brand fuel.

  • Adjusting the carburetor for optimum performance.

  • Contacting the equipment manufacturer for updated designs in air control baffling, mufflers, etc.

  • Checking the anti-afterfire solenoid for proper operation

  • If equipped with an anti-afterfire solenoid, shut engine off at full throttle.
    NOTE: This after fire solenoid is specified by the equipment manufacturer.

Backfire typically occurs when the engine is decelerated rapidly.

Some possible causes include:

  • Lowering engine speed too fast

  • Gasoline, which contains higher blends of alcohol

  • Carburetor adjustments set too lean

  • Muffler construction can induce backfire

  • Higher than normal engine temperatures

  • Some carburetors can induce backfire due to the sensitivity of internal transitional passages (This condition cannot be corrected).

Some possible cures include:

  • Lower engine speed slowly

  • Change brands of fuel to lower or non-alcohol

  • Adjust carburetor for optimum performance

  • Inquire with equipment manufacturer about increasing engine-cooling air volume by decreasing air restrictions.

In any event, your best source of information would be to consult your local Briggs & Stratton Authorized Dealer.

Your Briggs & Stratton Authorized Dealer has all the information relating to Briggs & Stratton warranty information, replacement engines, short blocks, parts, pricing, service/repair, specifications, etc.

For your convenience, we offer three easy ways to locate your nearest Briggs & Stratton Authorized Dealers:

  • Use our website's Service Center Locator.

  • Visit and enter "Lawn Mowers" or "Engines-Gasoline" in the Category search field and your Postal Code in the Location search field.

  • Call the Briggs & Stratton Automated Hotline at (800) 444-7774. This hotline is available 24 hours a day/7 days a week and features voice recognition technology to assist you in finding the Briggs & Stratton Authorized Dealers in your area. Automated maintenance tips, product information, and FAQs are also offered through voice activated menus.

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