How to Adjust a Briggs & Stratton Carburetor

Written by dan gaz
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Keeping your Briggs & Stratton mower engine running smooth is no easy task. One area to maintain regularly is the carburettor and linkages. Over time, debris and constant vibration can skew the speed and mixture in the carburettor, which leads to poor performance and black smoke from the exhaust. Some simple adjustments can be made in order to keep everything in your Briggs & Stratton engine running like new.

Skill level:
Moderate

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Things you need

  • Phillips screwdriver
  • Slotted screwdriver
  • Socket wrench set
  • Tachometer

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Instructions

  1. 1

    Remove the air filter and air cartridge with the engine off.

  2. 2

    Locate and turn the idle mixture screw clockwise until the needle barely touches the seat. Then, turn the same screw counterclockwise 1.5 turns.

  3. 3

    Turn the main jet adjustment screw (located at the base of the float bowl, if applicable) clockwise until the screw barely touches the seat just inside the emulsion tube. Turn that same main jet screw in the opposite direction 1-1.5 turns.

  4. 4

    Replace the air filter and air cartridge and start the engine.

  5. 5

    Run the engine for five minutes at half throttle. When the engine is warm, turn the idle mixture screw clockwise until the engine begins to slow. Turn the screw counterclockwise until the engine begins to slow again. Turn the screw clockwise until you reach the midpoint.

  6. 6

    Attach a tachometer to your engine (making sure to attach the red wire to the spark plug wire) and set the idle speed screw to bring the engine to either 1750 RPM or 1200 RPM for aluminium-cylinder and cast-iron cylinder sleeved engines, respectively.

  7. 7

    Idle the engine and hold the throttle lever against the idle speed screw to truly idle the engine.

  8. 8

    Repeat the adjustments on the idle mixture from Step 5 to fine-tune the mixture.

  1. 1

    Start the engine and run it at half throttle for five minutes. Stop the engine when it's sufficiently warmed up.

  2. 2

    Find the high speed mixture screw and turn it clockwise until the needle barely touches the seat. Turn the screw in the opposite direction 1.25-1.5 turns.

  3. 3

    Restart the engine and set the throttle to either "high" or "fast," depending on the make and model. Turn the high speed/main jet screw clockwise until the engine slows. Turn the screw counterclockwise until the engine slows again. Turn the screw clockwise to the middle.

  4. 4

    Move the throttle from "idle" to "fast" in order to check the engine acceleration. It should accelerate smoothly.

  5. 5

    Readjust mixture screws if engine does not accelerate smoothly.

  1. 1

    Remove the air filter and air cartridge, then locate the choke lever on either the engine or the speed engine controls.

  2. 2

    Move the lever to "fast" or "high," and loosen the cable mounting bracket with a slotted screwdriver to allow the cable casing to move freely.

  3. 3

    Close the choke by moving the cable casing and tighten the cable mounting screw. Check the motion of the control lever and repeat steps as necessary until the cable moves freely.

Tips and warnings

  • Briggs & Stratton recommends reading and abiding by the company's safety information document before performing any and all engine work.
  • This information is not meant to take the place of work performed by a Briggs & Stratton authorised dealer.

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