Small Engines Carburetor Problems and Solutions

Published on March 20th, 2015 | by Jacks

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Carburetor Problems and Solutions

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The following is a chart of potential carburetor problems and possible remedies. This chart is intended to be a helpful guide when troubleshooting your carburetor. Each incident varies in accordance to individual use. Regular inspection of carburetor parts is recommended.

Always consult your owner’s manual for specific Carburetor tuning and recommendations.

Check float shaft for wear and float for leaks or dents

PROBLEM POSSIBLE SOLUTION
  • Engine hunts (at idle or high speed)
  • Carburetor Leaks

Examine idle and main mixture adjustment screws and O-Rings for cracks and damage.

  • Carburetor out of adjustment
  • Engine will not start
  • Engine will not accelerate
  • Engine hunts (at idle or high speed)
  • Engine will not idle
  • Engine lacks power at high speed
  • Engine overspeeds
  • Engine starves for fuel at high speed (leans out)

Adjust main mixture adjustment screw; some models require finger tight adjustment

  • Carburetor out of adjustment
  • Engine will not start
  • Engine will not accelerate
  • Engine hunts (at idle or high speed)
  • Engine will not idle
  • Engine lacks power at high speed
  • Idle sped is excessive

Adjust idle mixture screw

  • Carburetor out of adjustment
  • Engine will not idle
  • Idle speed is excessive

Check for bent choke and throttle plates

  • Engine will not start
  • Engine hunts (at idle or high speed)
  • Engine will not idle
  • Engine overspeeds
  • Idle speed is excessive
  • Engine starves for fuel at high speed (leans out)

Adjust control cable or linage, to assure full choke and carburetor control

  • Carburetor out of adjustment
  • Engine will not start
  • Engine overspeeds

Clean carburetor after removing all non-metallic parts that are serviceable.

  • Carburetor floods
  • Engine starves for fuel at high speed (leans out)

Check inlet needle and seat for condition and proper installation

  • Carburtor leaks
  • Engine overspeeds
  • Idle speed is excessive

Check sealing of welch plugs, caps, plugs and gaskets

  • Carburetor out of adjustment
  • Engine will not idle
  • Engine lacks power at high speed
  • Carburetor leaks
  • Engine overspeeds

Adjust governor linkage

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  • Engine hunts (at idle or high speed)
  • Engine will not idle
  • Engine lacks power at high speed
  • Carburtor floods
  • Engine starves for fuel at high speed (leans out)

Adjust float settings if float type carburetor

  • Engine hunts (at idle or high speed)
  • Engine will not idle
  • Carburetor floods
  • Engine will not start
  • Engine will not idle
  • Engine lacks power at high speed
  • Carburetor floods
  • Idle speed is excessive

Check diaphragm for cracks or distortion and check nylon check ball for function if available

  • Engine hunts (at idle or high speed)
  • Engine lacks power at high speed
  • Carburetor floods
  • Idle speed is excessive
  • Engine starves for fuel at high speed (leans out)

Check sequence of gaskets and diaphragms for the particular carburetor being repaired



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About the Author

Jack's Small Engines has been providing parts for outdoor power equipment online since 1997. We also run a service center for outdoor power equipment like riding mowers, snow blowers, generators, chainsaws, and just about anything else.



12 Responses to Carburetor Problems and Solutions

  1. Alex Fuller says:

    Engine will not start using choke,will start manually choking with your hand what is theinitial carburetor settings

  2. B. Adkins says:

    The engine should start and run at any setting between 1 and 1 1/2 turns out from finger tight. Make sure the needle and seat are both clean before installing the needle, BUT be CAREFUL not to damage either by cleaning with metal (wire). After the engine warms up the idle can be fine tuned for optimal performance.

    Good Luck!

  3. Mark Norman says:

    Just found this site today, wish I had 2 weeks ago. My 12.5 Briggs/Murray mower is old but only
    recently have given me problems. I removed the carb and had it rebuilt for an external leak at the
    intake area, put it on and ran good but with an engine firing miss. Took the plug out and it was dripping with fuel.
    Is this a product of rebuild or is it time for engine work or replacement? Thanks for assistance -Mark N.

    • Daniel says:

      Sounds like the needle is not seating and/or the float needs replacement. Most of the floats in small engines do not have a metal tang to adjust them with unlike snowmobile’s, motorcycles, and outboard boat motors. You will have to take the carb off and dis-assemble it to verify.

      The other thing that could be happening is you are using too cold of a spark plug. To cold of a plug does not ignite all the fuel in the combustion area. If you use too hot of a plug it will overheat and cause detotonation and pre-ignition.

      Just a few things to look at.

  4. Carmine says:

    I have a lawnmower Craftman ( SEARSE) 6.2 horse power front wheel drive . I replaced the spark plug, filter, new carburator , new blade, clean the gas tank and line ,, new (fresh Gasoline ) I get no gasoline into the sparl plug chamber . Can you give me advice on WHY ? I am a retired man and try to safe a dollar . Than you for your understanding , The best Carmine

    • Daniel says:

      Make sure to adjust the pilot screw 1 to 1/2 turns out for initial setting. Verify that the governor linkage is correct. when the engine is off the butterfly should be open. if not that will have to be fixed first.

      Replace the fuel line first. If you use any fuel with ethanol that would be the first thing I would look at. If you are using a fuel filter verify the arrow on it is going to the carb.

  5. Rob says:

    I recently bought a pull behind brush hog. It has a 12.5hp B&S engine on it. I had to change the coil right away due to chipmunk damage. Now that it starts, it runs good, but the choke has to be left on and when I shut it off, it floods. If you try to keep starting it, the plug gets soaked and gas will seep out of the carburetor where the air filter and cylinder connect. There isn’t any gas in the oil. Any ideas?

  6. bob says:

    if I replace carburetor ,idle should be set to run

  7. Bryan says:

    I just replaced the carb on my Kohler engine. When I shut the mower off gas keeps flowing through the carb and runs out. What’s the dang deal?

    • Hi Bryan,

      Likely, you have the same problem as Jide below, I’d recommend checking out the float, pins and valves, be sure they are all properly functioning, if debris has gotten in to your needle valve it may be staying open, or it could be the float malfunctioning.

      Best of luck!

  8. Jide says:

    what could be responsible for putting fuel in the carb before an engine starts running

    • Hi Jide,

      The likely cause of this is if your float is malfunctioning. Unfortunately the only way to check this out is to remove the carburetor, clean it, and disassemble it. A problem with the float is also likely to cause flooding when trying to start the engine.

      Check the adjustment on your float pin, and maybe even get a new one, and this should hopefully stop your problem!

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