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  1. #21
    Veteran Member
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    AC WD 34 hp/3500 lbs MF 261 60 hp/5380 lbs

    Default Re: Stihl 261. Starts when cold. Fails to restart when hot.

    My Stihl MS 290 Farm Boss usually starts when cold but occasionally won't start when warm. At these times, it pulls very easy like it has compression release. Several people, including the dealer have suggested a sticky ring. I seldom use this saw and haven't gotten around to removing the muffler and checking the rings before the saw cools back down. I might just switch to Stihl brand oil and see if that solves the problem.

  2. #22
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    Default Re: Stihl 261. Starts when cold. Fails to restart when hot.

    Quote Originally Posted by Bfitzgerald3 View Post
    I reset the carb per the manual. I don't have a tach. Showing ignorance here... I would have no idea how to use it if I had one. If the problem happens again, i'm sure a neighbor wold have one to loan...If you have the time to share how to use it to set the thing up right, feel free...someone will definitely benefit from it.
    As requested.
    I do not have a 261 but use these on my Stihl saws. One an older 026 (forrunner of the 260/261/262) and a 460.
    These procedures are from two sources that are specified. One is the 026 Repair and Service Manual the other is the MS460 Workshop Manual.

    I do not know if they are applicable to your specific saw but should give a start hopefully.

    I really like the procedure from the 460 manual but have included the 026 procedure as well. The 460 low speed procedure may read confusing the first time but read a couple of times then it makes good sense.

    The procedures all state to have the saw warmed up. I can not stress that enough. Otherwise you are going nowhere with the adjustments.

    Stihl 026 Owner's Manual Carb adjustment procedure

    Carefully screw both the low speed screw (L) and high speed screw (H) down onto their seats.
    Now open the low speed screw one turn counterclockwise (standard setting).
    Now open the high speed screw one turn counter clockwise (standard setting).

    Warm up the engine.

    Engine stops while idling:
    'L' screw must be one turn open

    Turn the idle speed screw clockwise until the chain begins to run then back off the screw one quarter turn.

    Chain runs when engine is idling:
    'L' screw must be one turn open

    Turn the idle speed screw another quarter turn in the same direction.

    Erratic idling behavior, poor acceleration (even though 'L' screw in one turn open)
    Idle setting is too lean.
    Turn the low speed screw counterclockwise until the engine runs and accelerates smoothly.


    Stihl 026 Carb Adjustment Instructions from Service Manual using a Tachometer

    Note:
    Correct operation of the carburetor is only possible if atmospheric pressure and internal fuel tank pressure are equal at all times.
    This is ensured by the tank vent.

    Important: If problems occur on the carburetor or the fuel supply system, always check and clean the tank vent.


    Standard setting
    To readjust the carburetor, start with the standard setting.

    - Carefully screw down both adjusting screws until they are against their seats.

    Then make the following adjustments:

    H = High speed screw (1), open 1 full turn
    L = Low speed screw (2), open 1 full turn

    A slight correction to this setting may be necessary at high altitudes (mountains) or near sea level.

    For corrections to high speed screw (H):
    Use a tachometer - do not exceed max. permissible engine speed.
    Engine can be damaged by lack of lubricant and overheating.

    Maximum engine speed with bar and properly tensioned chain: 13,000 rpm (024) 14,000 rpm (026)

    Note: If no tachometer is available, do not turn the high speed or low speed screws beyond the standard setting to make the mixture leaner.

    Furthermore, the engine speed of machines with catalytic converter must not be less than 12,000 or 13,000 rpm.

    - Check chain tension.
    - Check air filter and clean if necessary.
    - Inspect the spark arresting screen and clean or replace if necessary.
    - Start the engine and warm it up
    - Adjust idle speed correctly (chain must not rotate).

    Turn high speed screw (H) and low speed screw (L) clockwise for leaner mixture at high altitudes or counterclockwise for richer mixture at sea level.

    Turn screws very slowly and carefully - even slight movements produce a noticeable change in engine running behavior.

    Note the following when making corrections to high speed screw:

    The setting of the high speed screw (H) affects the maximum off-load engine speed. If the setting is too lean, the maximum permissible engine speed will be exceeded and increase the risk of engine damage.

    Adjusting engine idle speed:
    A correction at the low speed screw (L) usually necessitates a change in the setting of the idle speed screw (LA) (3).

    Engine stops while idling:
    Check standard setting.

    Turn idle speed screw (LA) clockwise until the chain begins to run - then turn it back one quarter turn.

    Chain runs while engine is idling:
    Check standard setting.

    Turn the idle speed screw (LA) counterclockwise until the chain stops running - and then turn it about another quarter turn in the same direction.

    Erratic idling behavior, poor acceleration
    Idle setting too lean.

    Turn the low speed screw (L) counterclockwise until the engine runs and accelerates smoothly.


    From MS460 workshop manual

    Standard setting (without tachometer)
    To readjust the carburetor, start with the standard setting.
    Carefully screw down both adjusting screws (H and L) until they are against their seats.
    Then make the following adjustments:
    Open high speed screw (H) one full turn.
    Open low speed screw (L) one full turn.
    If no tachometer is available, do not turn the high speed screw (H) beyond the standard setting to make the mixture leaner.

    Standard setting (with tachometer)
    Check the air filter and clean or replace as necessary.
    Check and clean or replace spark arresting screen (if fitted).
    Check chain tension.
    Warm up the engine.
    Adjust idle speed.

    Adjusting idle speed
    Adjust idle speed with a tachometer. Adjust specified engine speeds within tolerance of +/- 200 rpm.
    1. Adjust engine speed with idle speed screw (LA) to 3,300 rpm.
    2. Turn low speed screw (L) clockwise or counterclockwise to obtain maximum engine speed.
    If this speed is higher than 3,700 rpm, abort the procedure and start again with step 1.
    3. Use the idle speed screw (LA) to set engine speed again to 3,300 rpm.
    4. Set the engine speed to 2,500 rpm with the low speed screw (L).

    Starting from the standard setting, use the high speed screw (H) to adjust the maximum engine speed
    to 13,500 rpm. If the setting is too lean there is a risk of engine damage due to insufficient lubrication and overheating.

    Additional comment: The 026 manual does not really address and the 460 manual addresses it inadequately IMO how to adjust the high speed screw.

    Below is my technique and only a technique.

    Engine high RPM too low or too high:
    Note: Do not run the engine WOT unloaded for more than a second or two, burp the throttle to determine the engine RPM at full throttle. Always use a tachometer.
    WOT RPM above specification: mixture is too lean turn high speed screw counterclockwise.
    WOT RPM below specification: mixture too rich turn high speed screw clockwise.

    The 026 has a discrepancy between WOT RPM spec 13,500 or 14,000. I error on the 13,500 side.
    The 460 spec is 13,500. Determine what yours is for the 261 but will likely be 13,500.

  3. #23
    Platinum Member
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    Covington, GA
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    JD 870

    Default Re: Stihl 261. Starts when cold. Fails to restart when hot.

    The big thing to know is that you want the high speed to be on the rich side not the lean side. Lean may run hotter and the cylinder may score. Most folks unless they are tool nerds do not have a tachometer in their toolbox. I have this one. You just hold it close to the spark plug to get a reading.
    DTI Tech Tach TT-20K Small 2 Cycle Two Stroke Tachometer

  4. #24
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    West Cascades Washington State
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    PT 422

    Default Re: Stihl 261. Starts when cold. Fails to restart when hot.

    Quote Originally Posted by JimRB View Post
    The big thing to know is that you want the high speed to be on the rich side not the lean side. Lean may run hotter and the cylinder may score. Most folks unless they are tool nerds do not have a tachometer in their toolbox. I have this one. You just hold it close to the spark plug to get a reading.
    DTI Tech Tach TT-20K Small 2 Cycle Two Stroke Tachometer
    When i tuned mine, WOT turned it richer till it started to miss. That is if you don't have a tach.

  5. #25
    Veteran Member s219's Avatar
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    Kubota L3200

    Default Re: Stihl 261. Starts when cold. Fails to restart when hot.

    I normally tune by ear, so that the saw warbles (two-strokes) at WOT with no load. In the wood, it drops RPM just enough to settle out.

  6. #26
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    Default Re: Stihl 261. Starts when cold. Fails to restart when hot.

    Quote Originally Posted by s219 View Post
    I normally tune by ear, so that the saw warbles (two-strokes) at WOT with no load. In the wood, it drops RPM just enough to settle out.
    I used to tune by ear but my ear is not what it used to be (maybe never was) and I was 1000 rpm low when I checked it after getting the tach a while back.

  7. #27

    Default Re: Stihl 261. Starts when cold. Fails to restart when hot.

    I really like these instructions for tuning:
    Chainsawr Adjustment and Tuning of a Chainsaw Carburetor

  8. #28
    Veteran Member CHDinCT's Avatar
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    Kubota BX25

    Default Re: Stihl 261. Starts when cold. Fails to restart when hot.

    Stupid question maybe, but when it says to turn the L or H screw one turn, is that 360* or 180*? Pretty sure it's 360 but I've never seen it fully described. With a slot head screw, 180 sort of looks like "one turn".
    Chris

    2 acres and a mule, er, Kubota BX25, and too many other toys,er, tools to list.

  9. #29
    Elite Member TomSeller's Avatar
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    Default

    Quote Originally Posted by CHDinCT View Post
    Stupid question maybe, but when it says to turn the L or H screw one turn, is that 360* or 180*? Pretty sure it's 360 but I've never seen it fully described. With a slot head screw, 180 sort of looks like "one turn".
    360, but good question. Kinda takes two finger turns to make one screw turn.

  10. #30
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    Kubota, JD and a Grillo

    Default Re: Stihl 261. Starts when cold. Fails to restart when hot.

    Hard starts when hot usually means exhaust restriction. Does it have a spark arrestor screen? Remove it... Blow out the muffler also.

    Take the carb off, remove everything including the float needle and flush it out with carb cleaner, then blow it out again with compressed air. Check all rubber parts, no cracked diaphragm, good fuel line, good seals etc. Gasoline should be premium or a high octane like 93 and less than 6 weeks old. Never leave fuel in the saw for more than a week or so.

    I've been burned by so called dealers to many times. I just make time and fix my own stuff. Has an old Stihl blower that needed cleaning up, the dealer charged my Father $50 and didn't even clean check the spark pug or clean the spark arrestor. I went over it and found a bad pull rope needing attention, poorly installed fuel line that was leaking and sucking air, filthy muffler and a well worn spark plug. Dealer couldn't figure out what was causing the low power, they replaced the air filter and the leaking fuel line for $50... I though they were professionals... wrong.

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