How to tune a chainsaw carburetor

Written by josh nuttall
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How to tune a chainsaw carburetor
MS 441 C-Q STIHL Magnum™ Chain Saw (http://www.stihlusa.com/chainsaws/MS441CQ.html)

All chain saws arrive at the sales floor from the factory with their carburettors preset to an ideal running setting. It is possible though that one of the adjusting screws may loosen and throw off the high or low speed setting. Adjustments are easily made, so don't fear. Also, adjustments will be necessary in the following situations: the engine stops while idling, or the chain creeps while the engine is idling; the engine idle is choppy or the acceleration is poor; the chainsaw will be used in high altitudes.

Skill level:
Easy

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Things you need

  • Small flathead screwdriver
  • Extra fuel-oil mixture
  • BernzOmatic torch
  • Igniter

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Instructions

  1. 1

    Start the engine and let it run long enough to warm it up (usually 2 - 3 minutes is sufficient). Shut off the engine.

  2. 2

    Locate the adjustment screws near the carburettor labelled with an "H," an "L," and an "LA." The "H" screw adjusts the high speed fuel-air mixture; the "L" screw adjusts the low speed fuel-air mixture; and the "LA" screw adjusts the idle speed.

  3. 3

    Check the air filter to see if it is clean, and if it is not, replace it. Check the spark arrest filter in the muffler to be sure it is clean; clean the spark arrester if it is dirty by removing it and burning the deposits off with a BernzOmatic torch, or other torch. Replace the filter if it is in really bad shape.

  4. 4

    Turn the "H" screw counterclockwise until it stops (should be no more than a 3/4 turn with a small flathead screwdriver. Turn the "L" screw clockwise until it stops. Then turn it counterclockwise 1/4 turn.

  1. 1

    Be sure the carburettor is set to the standard setting. Start the engine.

  2. 2

    Turn the "LA" screw clockwise until it stops, or until the chain begins to run. Turn the screw counterclockwise 1 x 1/2 turns.

  3. 3

    Call your local chainsaw repair shop to have them repair the chainsaw if the chain continues to run after completing Step 2.

  1. 1

    Be sure the carburettor is set to the standard setting. Start the engine.

  2. 2

    Verify that the low speed screw "L" is 1/4 turn open.

  3. 3

    Turn the low speed screw counterclockwise until the engine idles and accelerates.

  4. 4

    Verify that the new setting works after the engine has cooled and warms up again.

  1. 1

    Verify that the standard setting is in place.

  2. 2

    Start the engine and allow it to warm up.

  3. 3

    Turn the high speed screw "H" clockwise slightly (making the mixture leaner). Do not attempt to turn the screw any further than stop. The engine should run satisfactorily after this adjustment.

Tips and warnings

  • You usually have to adjust the idle speed setting "LA" whenever you change the low speed setting "L."
  • Keep the chainsaw blade away from people and property while the engine is running and you are adjusting the carburettor.

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