FAQ SUPPORT

Backfire/Antifire from Carburetor or Muffler

What causes engine backfire out of the carburetor or muffler?

"Backfiring" is a condition described as a loud bang, poof, explosion, etc. when idling the engine down, or after the engine has been shut off.

(Note: "After-fire", and/or "back-fire" will not harm the engine at all!)

"After-fire" occurs after the engine has been shut off.

Some possible causes include:

1. 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.

2. Gasoline that contains alcohol has a tendency to ignite easier, plus cause the engine to run slightly hotter. This, combined with a hot muffler, can cause after-fire.

3. The type of muffler that has been installed by the equipment manufacturer may cause after-fire.

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

5. If anti-after-fire solenoid is installed it may not be working properly.

Some possible cures include:

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

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

3. Adjusting the carburetor for optimum performance.

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

5. Checking the anti-after-fire solenoid for proper operation.

6. If equipped with an anti-after-fire 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:

1. Lowering engine speed too fast

2. Gasoline, which contains higher blends of alcohol

3. Carburetor adjustments set too lean

4. Muffler construction can induce backfire

5. Higher than normal engine temperatures

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

Some possible cures include:

1. Lower engine speed slowly

2. Change brands of fuel to lower or non-alcohol

3. Adjust carburetor for optimum performance

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

In any event, your best source of information for any engine concern would be a Briggs & Stratton Authorized Dealer.

Please read and abide by any applicable Safety Information contained in your engine Operator's Manual. The material provided above is not intended to replace work performed by a Briggs & Stratton Authorized Dealer. Terms and Conditions apply to all of the information presented on this website. Always be sure to completely read and understand your engine Operator's Manual.

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