Chainsaw Carburetor Tuning 101

MasterMech Posted By MasterMech, Mar 1, 2013 at 9:07 PM

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  1. MasterMech


    AFAIK - The MS290 uses a standard flat-head screwdriver for carb adjustments. The only tool required may be the one used to remove the limiter caps on the carb.
  2. MasterMech


    The saw should run upright, upside down, standing on-end, or lying on its side equally well. Letting it idle for 30 seconds doesn't really do anything for it either. If the saw stalls or changes rpm when it changes position, the crankshaft bearings/seals are most likely worn and/or leaking and should be replaced. Pressure/vacuum test to confirm.

    No it won't. The L screw only affects the amount of fuel delivered with the throttle closed or partially open.

    Again, incorrect. The inlet needle valve and the diaphragm control fuel flow into the carburetor. This happens automatically and requires no routine adjustment from the operator.

    When setting the final idle rpm's, the L screw is generally set quite rich to prevent the saw from leaning out excessively on decelleration. This is what I'm doing in the video at aprox the 02:10 mark. The L and LA settings should be finalized before moving on to the H setting because the L setting will affect the H setting but not vice-versa.

    I totally agree with cleaning the air filter and the muffler screen. Should be done before you begin tuning. Also, you should reset to factory default carb settings (if known) before getting started.
  3. HDRock

    Minister of Fire

    Oct 25, 2012
    Grand Blanc, Mi
    The only factory default settings I can find for the 445 are
    Maximum power speed – 9600 RPM
    Maximum recommended engine speed – 13,000 RPM
    Idle speed – 2700 RPM
    If I had a tach , would I be trying to set the high RPM 9600 and not exceed 13,000 ? If not, What do they mean by the maximum power speed ?
    in the manual they don't give you the number of turns to start with, because they don't want you adjusting the saw,I see most saws are 1 to 1 1/4 out to start
  4. MasterMech


    9000 RPM will be where the saw makes the most power.

    13000 RPM will be what you set the H setting to.

    You can tune so long as you can get the saw started. A bit easier if it's somewhat close to start with however.
  5. pyroholic


    Feb 17, 2013
    Are the numbers (rpm) and process for the L and LA settings going to be the same for all Stihl's with the only variants being the max rpm? If not where is this info at? specifically looking for specs for the 038 magnum, but need to know for my other saws too.
  6. MasterMech


    The specs are generally in your owners manual. Your 038 will tune exactly like the 460 in the vid but your factory max rpm is 12500 I believe. I would tune it by ear first and see where you end up. If you have it set at 13k or less and it's four-stroking out of the wood, I wouldn't worry about fattening it up to 12500. ;)
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