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Stihl Chainsaw Carburetor Adjustment

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Stihl chainsaws’ have three carburetor adjustment screws

(LA) Idle Speed screw - This controls the engine speed at idle. If set too low, the saw will die. If set too high the chain will run. This is dangerous.

(L) Low speed adjustment screw - This is the low speed jet. This is the adjustment that controls the air/fuel mixture at idle. Adjust this screw too rich and the chainsaw will blubber and die at idle speed. Adjust this screw too lean and the engine will starve. The saw will race or surge. An extremely lean adjustment will also cause the engine to die.

(H) High speed adjustment screw - This is the high speed jet. This is the adjustment that controls the air/fuel mixture at high RPMs. Adjust this screw too rich and the chainsaw will blubber, too lean and it will over rev

Safe Basic Settings

Screws (H) & (L) - Turn the adjustment Screws (H) & (L) down onto their seats (clockwise). Back them off 1 complete turn (counter-clockwise)
Screw (LA) - Turn (LA) Idle Speed screw until the chain stops. Then turn counter-clockwise one quarter of a turn.

Fine Tuning – Screw (L)

Erratic idling behavior; poor acceleration - Idle setting too lean; turn low speed adjusting screw (L) counterclockwise until engine runs and accelerates smoothly. Readjust screw (LA).

Exhaust smokes at idle speed -Idle speed setting too rich; turn low speed adjusting screw (L) clockwise until engine speed drops. Then turn screw back one quarter turn and check that engine still accelerates smoothly when you open the throttle. Readjust screw (LA).

SCREW(H)—CAUTION!

chainsaw carburetor adjustment

Adjustment of the high speed adjusting screw(H)not only affects the power output but also the maximum off-load engine speed. If the setting is too lean (screw turned too far clockwise), the maximum permissible engine speed will be exceeded. This can cause engine damage, brought about by lack of lubrication and overheating in particular. Corrections to the setting of the high speed adjusting screw may be carried out only if an accurate tachometer is available to check the maximum engine speed of 13,000 rpm (with bar and correctly tensioned chain).

When the engine is tested at the factory the carburetor is set to obtain a slightly richer mixture to ensure that the cylinder bore and the bearings receive additional lubrication during the break-in period. This setting should be left as it is for the first three tank fillings. The high speed adjusting screw may then be turned no more than 1/4 turn clockwise (leaner mixture). Caution: The engine”s maxi­mum permissible rpm must not be exceeded! Note that even slight alterations on the adjusting screws have a noticeable effect on the engine”s running behavior. Only carry out carburetor adjustments after cleaning the air filter and warming up the engine.

If you have no means of checking the maximum engine speed, do not set the high speed adjusting screw (H) any leaner by turning it (clockwise) beyond the basic setting Above!

« Stihl Chainsaw Carburetor Tuning ChartStihl Chainsaw Troubleshooting Guide »

Stihl Carburetor Part BreakdownThis how-to works with a Husqvarna, husky, Jonsered, Poulan, McCulloch, Craftsman, Homelite, Echo chainsaws as well as a Stihl 009, 009L,011, 011T,012, 017, 018, 018C, 019, 019T, 020, 020AV, 020T, 021, 023, 024, 025, 026, 026 PRO, 028, 029, 034, 036, 036 PRO, 036 QS II, 039, 044, 046M, 066M, 088M, MS170, MS180C, MS191T, MS192T, MS200, MS200T, MS210, MS250, MS260, MS260 PRO, MS270, MS280, MS290, MS310, MS360, MS360 PRO, MS360 QS II, MS361, MS390, MS440, MS460, MS660, MS880, HT100, HT101, HT70, HT75 STIHL – Virtual factory visit

  • Anonymous

    Thanks for your input David. Most of the comments on this post got jumbled when I moved to Disqus. I was able to repair most, but your comment was lost.

  • Anonymous

    (Edited by a moderator) explanation: Most of the larger comments on the post were truncated when I move the comments to Disqus. I edited no ones comments I just tried restored them to the original.

    David thanks for your input it is helpful I changed this guide because of your comment, and I urge readers to look over all the comments on this page you’ll find lots of useful information.

  • Frank California

    I just downloaded the pdf file for the 017 from http://www.stihl.com they will even mail one to you if you like

  • Anonymous

    Sounds like the rings have seized to the cylinder wall, this happens a lot after storage. A little air-borne humidity has gotten into your engines cylinders causing the pistons to seize up. Take out the plug and give it a try, If your lucky your muffler is clogged. Get a good penetrating lubricant and spray it into the cylinder and let it go to work, after several hrs-days try to turn the engine over. Work it at the crank not the pull cord. Go slow.

  • Anonymous

    Great saw Derek. twodogs maybe right if their is no scoring it could be starving for fuel. try a new plug with the correct gap clean the tank, fuel line, and carburetor thoroughly.

  • Hansumboy4u

    034 ur cylinder is full of fuel when the plug is in it wont pull over ppl it over with the plug out realy fast about 20 times and then put plug it and don’t choke it ur carb it needs a kit put in it diaphragm and needle

  • Jaimegarciaramirez

    I have a Wrigley’s 025 starts on choke but when I push thaw lever for moral start it shuts off

  • Roy

    buy her an electric chain saw and a long extension cord. It’ll start everytime.

  • Thedodgeman899

    i have a newer 029 that died when was using it and now will not start or fire any clue how to get it to work?

  • Johnny varnadore

    you can still find the points but u are going to have to sent it to sihl to get them set proprley i own a small engine repair bussiness ive been doing it for over 20 years and iv always sent it to the factory but if u can set them u can come work for me

  • Johnny_brvo2u

    i dont have valves

  • Johnny_brvo2u

    thanks to ethonol for the white gunk u are going to have to take your carb all the way down idel screws and all leave the welch plugs in get u a can of carb cleaner spray every hole u see put it all back together idel screws go all the way in back out two and a half turns thats a starting point for yor h and l make sure the gasket goes on first then the diphram hope this helped johnny’s small engine repair and service llc

  • Blomberg

    Had ms 192 c-e light weight saw for 2 years, worked fine until it quit. Found Welch plug in Zama carb had dropped out. It was cemented in and not punched. Tried to cement in with Permatex #2, ran 10 minutes and quit. Plug had fallen out again, cement dissolved in gas. So made and used oblong punch to set Welch plug followed by tiny amount of old bottle of clear nail polish around edge. Dried overnight. Saw has been running with good power last two weeks. Gasoline with alcohol dissolves most cements. Have Seal-All from ACE on hand in case have to cement plug again.

  • Anonymous

    Have you determined whether or not you have spark? That would be the first step. Pull the plug out, connect it to the plug wire, and let it touch a metal part of the saw. Then pull the cord while watching the electrode on the plug. If it sparks, chances are that the ignition is ok and we can go further. If not, you have ignition problems.

  • Anonymous

    Sounds like an air leak. If you can run an engine on full choke, you definitely have an air leak somewhere, you would have to have the mixture screw bottomed out to run that lean. check to make sure the carburetor screws are tight. If those are good check the cylinder bolts are tight too. An old trick to find a vacuum leak is to get it running and spray choke or carb cleaner around it–when the revs go up listen for a change in exhaust note. If no air leak are found the carburetor may have a problem and need to be rebuilt.

  • Jphogg

    jeff have 390 ms shoots gas from carb why?

  • http://craniumcastle.com/user.php?login=botelhokenneth&view=history Nicole Snider

    Interesting blog. It would be great if you’re able to provide additional information regarding it. Thanks lots

  • ED K

    SPARK ARRESTER SCREEN MAY BE CLOGGED , REMOVE AND CLEAN .

  • http://public.sitejot.com/leejudy162.html Micha Duke

    I became just browsing here and there but happened to be you just look at this post.

  • Tjones399

    Derek, I just had the same issue. I rebuilt the walbro carb on my stihl 026, new gaskets, replaced the screen you were talking about. I also used a can of carb and choke cleaner and sprayed it thru all the holes. Even removed the high and low needle valves and sprayed thru them. I re-assembled the carb (great video on you-tube). But I also replaced the fuel line and filter. It started on the second pull woooohoooo. Make sure you get the correct fuel line. If yours is an older stihl you may need the straight fuel line, not the one with the pre-bend in it. Also check your fuel tank vent. If it is clogged it wont let the carb pull gas. Also when looking at your carb from the handle make sure the impulse line (right side bottom) is fully attached to the carb. Now reassemble and seat the L and H screws Clockwise to stop. Back each one out 1 1/4 turns left. Now choke and start. Again search youtube for stihl 048 carb rebuild video.. very helpful.

  • Bearh3526

    Gentleman, need help. I been in small tools for 20. Mostly partner and large construction equipment as well as small tools. Here the problem, have a Stihl TS 460 on the bench came in not running. Been sitting. Actually looks like someone found it at the bottom of a lake. Anyway, torn it down cleaned it up. Low compression, so replaced piston and jug and rings. Compression back up. Replaced carburetor with new one. Clean gas tank and replaced filter and fuel lines.
    Problem is I can not get any fuel to pump to the carburetor. have a clear fuel line. Did a pressure test on fuel line and tank no leaks. Did a leak down test on Piston and jug. Tested ok. Also did a pressure test on new carb just to make sure no leaks. So I figure I should have had a leak some where. Still scratching my head. Can any one give me something else to look for or do. Oh yes replace plug and yes I fired it up with direct gas to carb and it ran on that fuel only and shut off

  • Frank

    I’ve been working on the same problem for about a week with a Stihl 028. I’ve rebuild the carb several times, cleaned it out, and it still only runs when I spray gas in the carb. I have to believe it is a problem with the carb, but I’m scratching my head as well.

  • Anonymous

    Sounds like you have all the bases covered but here goes.
    Change the fuel line and filter if the fuel line has a pin hole in it, the engine will suck nothing but air.
    If the fuel diaphragm has a hole in it, it won’t suck in gas either.
    Also blow through the supply hose from the tank to make sure it isn’t plugged.
    If you still can’t get air through, try to follow the fuel’s path, and blow though each hole with compressed air. You should be able to find the obstruction that way.
    Look through the carb and you should see the reed valve. This is a piece of springy metal that covers the hole. Press on it gently to see if it can move towards the crank case. If not, the valve is stuck and fuel can’t get in.
    Make sure you are using the correct fuel/oil mixture.
    Seat it mixture screw all the way in gently return to position.

  • Muleskinner750

    what are the carb screw settings for an stihl 015L?

  • Jason

    I have a brand new stihl ms290, have run roughly 5 tanks of gas through it. The saw starts fine and runs fine as long as it is horizontal or with the bar tipped up. When I tip the bar down it sputters out. Proper mixture of gas that is new within the last month…any suggestions?

  • Tjones399

    Take the carb out and rebuild it with a gasket kit. Pay carefull attention when dis-assembling it so you rebuild it with correct gasket placement. Ebay is a good place to find kits or the walbro website. Also replace needle valve and make sure the spring is centered under the metering arm and the screw is tight that holds down the metering arm. If you still have problems check your fuel tank vent and make sure spark screen in the muffler is clean. Sounds like the needle valve is not closing and opening properly letting fuel run down thru the intake manifold. Really if the saw is brand new Stihl should repair it for you for free…Should be under warrenty..

  • Tankersley Dusty

    Hi to who ever might help! I have a ms390 I had a bad fuel line witch burnt up cylinder and piston. So I got a new piston and cylinder (non stihl) and took it too a stihl dealer and they put it together. And adjusted carb. It ran good for a bit(few minutes) now it dies when I give it throttle? But still idles fine! What’s wrong?

  • Crawfjames

    hi i have a stihl 009 was going strong but now it starts sometimes idles then when u go 2 peak the revs the saw cuts out. have cleaned the carbi and filter but still no go, can any1 help with advice and help me with the (L) AND (H) settings please

  • Redtick696969

    I have an 028 stihl that wont start well runs for 2 seconds lol!!!!! I changed fuel, air filters and spark plug fuel lines it had sat fer 6 years!! and the h and l screws were not in it i cleaned carb too

  • Anthony

    IMPULSE HOSE

  • Jayarnold24

    I have an old stihl 041 AV. I started it up ran two tans a half tanks of gas through it and all of a sudden it started bogging down when I tried to rev it up to cut. Thought it might be too hot so let it cool down and cleaned it up. After checking the air filter and a cool down, it starts up fine but again I can not get it to roar to life just idle. Please help.

  • Jayarnold24

    I have an old stihl 041 AV. I started it up ran two tans a half tanks of gas through it and all of a sudden it started bogging down when I tried to rev it up to cut. Thought it might be too hot so let it cool down and cleaned it up. After checking the air filter and a cool down, it starts up fine but again I can not get it to roar to life just idle. Please help.

  • DaveDell

    My Stihl Farmboss 290 has always (2 yhears now) balked at full size cuts. It runs fine. Cuts smaller branches. If I engage any more than about 6 inches of the saw it bogs down and doesn’t cut. It does this regardelss of blade/bar combination. It’s sharp. The exhaust port and spark screen is clean as a whistle. Actually, it’s suspiciously clean with hardly any darkening of the spark screen let alone any carbon deposits. It starts and runs great with smooth accelleration. I can’t adjust the hi end to a richer setting (counter clockwise – out) because it hits a stop at the 3/4 turn. Adjusting the low end makes no difference in either direction. Adjusting the high end leaner (clockwise to less than the recommended 3/4) makes no difference. It idles fine.

    I’m using a 20 inch bar and chain. One of those low kickback chain/bar combinations with 11 teeth on the roller. It’s the ones that came with the saw new. Would going to a 10 tooth roller and chisel blade help? Would going to a 16 inch blade help?