Stihl Chainsaw Carb Adjustment: Settings by Model, Per Manuals

There is no single Stihl carburetor setting. The Stihl manuals give different standard settings by model: the MS 271 and MS 291 use H out up to 3/4 turn and L out 1/4 turn, the MS 250 uses L out 1 turn, the MS 170 and MS 180 have only an idle screw, and the MS 261 C-M has no screws at all. Below are those manual procedures, plus when to stop and see a dealer.

Understanding the Stihl Chainsaw Carburetor

Every Stihl manual in this guide says the same thing about the carburetor: it leaves the factory with a standard setting that gives an optimum fuel-air mixture. What differs is how many screws you can touch and where they should sit. Three labels matter:

Screw	What it does	Source
H (high speed)	Sets the mixture at full throttle. The MS 250 manual says changing it alters the engine’s power output and its maximum off-load speed. Leaner means clockwise.	MS 250 manual
L (low speed)	Sets the mixture at idle and low throttle. Turning it counterclockwise enriches the mixture when idle is erratic.	MS 250 and MS 271/291 manuals
LA (idle speed; LD on MS 170/180)	Sets idle rpm so the chain stays still. The MS 170/180 idle screw has a left-hand thread.	MS 170/180, 250, 271/291 manuals

That last row corrects a common mix-up. Many guides call the idle screw “T”, which is another maker’s label. On a Stihl, look for LA or LD stamped beside the screw, and check your own model manual.

Stihl Carb Adjustment Chart: Settings by Model

This chart contains only models whose Stihl owner’s manual I read for this update. I left out every other model on purpose: a made-up number on a fuel-metering screw can damage an engine. For other models, use your own manual or ask a Stihl dealer.

Model	Carb screws in the manual	Standard setting (from the manual)	Idle spec	Manual
MS 170, MS 170 C, MS 180, MS 180 C	Idle screw LD only	Screw LD down counterclockwise (left-hand thread) until firmly seated, then 2 turns clockwise (LD = 2)	2,800 rpm	0458-207-0121-A
MS 210, MS 230, MS 250 (carburetor with H = 1 and L = 1)	H, L, LA	Both screws down onto their seats (clockwise), then H 1 full turn counterclockwise and L 1 full turn counterclockwise	2,800 rpm	0458-208-0121-C
MS 210, MS 230, MS 250 (carburetor with H = 3/4 and L = 1)	H, L, LA	H counterclockwise to the stop (no more than 3/4 turn); L clockwise to the stop, then back 1 turn	2,800 rpm	0458-208-0121-C
MS 271, MS 291	H, L, LA	H counterclockwise to the stop (max. 3/4 turn); L clockwise to the stop, then 1/4 turn counterclockwise	2,800 rpm	0458-574-8321-E
MS 261 C-M	None (M-Tronic)	No manual setting. The saw adjusts itself; see the M-Tronic section below	2,800 rpm	0458-153-8321-C

Myth check: the popular “L 1.5 turns, H 1 turn, idle 2,800 rpm for every Stihl” chart does not appear in any of these four manuals. I searched all four for “1.5” and “1 1/2” turns and found none. Idle speed is the one number that matches (2,800 rpm). Older models such as the 021, 025, 026, 034, 041, MS 260 and MS 290 are not covered here because I did not verify their manuals.

“Do not make the mixture leaner to achieve an apparent increase in power – this could damage the engine.”

Signs Of Carburetor Adjustment Need

Before you touch any screw, rule out the cheap causes. Stihl’s manuals tell you to check the air filter first, and to check the spark plug first when the engine is down on power, hard to start or runs poorly at idle. Then match your symptom to the manual’s own fix:

Symptom	What the manual says	Fix
Engine stops when idling	Idle speed too low	Turn LA clockwise until the chain begins to rotate, then back off by the amount for your model (see the idle section below)
Saw chain rotates at idle	Idle speed too high	Turn LA counterclockwise until the chain stops, then the extra turn for your model. If it still turns, see a servicing dealer
Erratic idle, poor acceleration (despite the standard setting)	Idle mixture too lean	Turn L counterclockwise a little at a time until the engine runs and accelerates smoothly, but no further than the stop. Then recheck LA
Down on power at high altitude	Setting may need a small correction	Make the standard setting, warm up, turn H slightly clockwise (leaner), no further than the stop. Restore the standard setting after you come down
Down on power, hard to start, rough idle	Not necessarily the carburetor	Check air filter, spark plug and spark arresting screen first

How to Adjust the Stihl Chainsaw Carburetor: Step-by-Step

Step 1 – Preparation and Safety

The Stihl manuals call for sturdy, snug clothing with cut-retardant protection, cut-resistant safety shoes with steel toe caps, tight-fitting safety goggles (EN 166) or a face shield, hearing protection, and sturdy protective gloves. Work on a level surface with firm footing, keep other people out of the working area, and never start the saw in an enclosed space or within 3 meters of where you refuelled. Engage the chain brake before starting and make sure the chain cannot touch the floor or any object. Switch the engine off, then check the air filter and clean or replace it if needed.

Step 2 – Make the Standard Setting for Your Model

With the engine off, find your model in the chart above and make exactly that standard setting. On the MS 271 and MS 291, for example, you turn H counterclockwise as far as it goes (max. 3/4 turn), turn L clockwise as far as it goes, then back it out 1/4 turn. If your model is not in the chart, use your model manual. If the screws are under plastic or metal caps, stop here and read the limiter section further down.

Step 3 – Warm Up and Set the Idle With LA

Start the engine and let it warm up. The idle is right when the engine keeps running and the saw chain does not rotate. Use the model-specific turns in the idle section below. If the chain keeps rotating at idle even after adjustment, Stihl says to have the saw checked by a servicing dealer.

Step 4 – Fix an Erratic Idle With L

If idle is erratic or acceleration is poor even with the standard L setting, the manual says the idle mixture is too lean. Turn L counterclockwise carefully until the engine runs and accelerates smoothly, but no further than the stop. Readjust LA afterward.

Step 5 – Leave H Alone Unless You Need an Altitude Correction

H is the screw that tempts people to chase power, and it is the one that can hurt the engine. The manual’s only H correction is for high altitude: standard setting first, engine warm, then H slightly clockwise (leaner), no further than the stop. It warns that a setting that is too lean raises the risk of engine damage through lack of lubrication and overheating, and that you should restore the standard setting after descending.

Step 6 – Test and Verify

Check for a steady idle with the chain still and clean pick-up. If you own a tachometer, confirm idle near the 2,800 rpm the manual lists. See our chainsaw tachometer comparison for how to hook one up.

How to Adjust the Idle on a Stihl Chainsaw

Idle adjustment uses only the idle screw (LA, or LD on the MS 170 and MS 180). The procedure is the same shape on every model, but the amount you back the screw off afterward is not, and that is where copied advice goes wrong. First make the standard setting and warm up the engine, then:

Model	Engine stops at idle	Chain rotates at idle
MS 170 / 180 (LD)	Turn LD slowly clockwise until the chain begins to rotate, then back off 1/2 turn	Turn LD slowly counterclockwise until the chain stops, then another 1/2 turn the same way
MS 210 / 230 / 250 (LA)	L to the standard setting, then LA clockwise until the chain begins to run, then back off 1/4 turn	L to the standard setting, then LA counterclockwise until the chain stops, then another 1/4 turn
MS 271 / 291 (LA)	LA clockwise until the chain begins to rotate, then back 1 turn	LA counterclockwise until the chain stops, then another full turn the same way

The same adjustment is 1/4 turn on one saw and a full turn on another, so use your own manual’s number.

If the screws were turned randomly and you have lost your baseline, our guide to adjusting a chainsaw carburetor from scratch covers that case for any brand. This guide stays on the manual procedures for specific Stihl models.

What Is the High RPM Setting on a Stihl Chainsaw?

There is no high-rpm number to dial in on the H screw. The manuals list rated power at a given speed instead: 3.5 hp at 9,500 rpm for the MS 271, 3.8 hp at 9,500 rpm for the MS 291 and 3.1 hp at 10,000 rpm for the MS 250. They publish no no-load top speed, and Stihl says only that H changes maximum off-load speed. Use the standard setting and the altitude correction only when you need it.

Stihl Saws With No Carb Screws (M-Tronic)

Some current Stihl saws have no H or L screw to turn. The MS 261 C-M manual says the chain saw automatically adjusts to the optimum power during operation, and that the M-Tronic version is shown on the approval label (for example, “M3.0” means version 3.0). What you can do depends on that version:

• Below version 3.0: speed up adaptation by carrying out five uniform cuts to length at full throttle.
• Version 3.0 or higher: calibrate the saw. With the chain brake engaged, start the engine without pressing the trigger and let it run 30 to 60 seconds, release the brake, then fully press and hold the trigger until the engine speed audibly drops, and release. The manual warns that the chain may rotate when the brake is released, so follow the full steps in your own manual.

If the engine repeatedly stops during calibration, Stihl says to engage the chain brake, stop using the saw and consult a servicing dealer. M-Tronic saws also tolerate more ethanol: the manual says up to 27 percent alcohol (E27), while engines with manually adjustable carburetors should not run gasoline above 10 percent alcohol.

Maintenance and Troubleshooting

A carburetor that will not hold its setting is often reacting to something else. Use the manuals’ own checks, in this order:

Check	What the Stihl manuals say
Air filter	Check it before any carburetor adjustment. Wash a caked filter in a clean, non-flammable liquid such as warm soapy water, dry it, and always replace a damaged one.
Spark plug	If the engine is down on power, hard to start or runs poorly at idle, check the plug first. Fit a new plug after about 100 operating hours, or sooner if the electrodes are badly eroded. Use only the suppressed type Stihl approves (Bosch WSR 6 F on the MS 210, 230 and 250; Bosch WSR 6 F or NGK BPMR 7 A on the MS 170, 180, 261 C-M, 271 and 291; electrode gap 0.5 mm).
Spark arresting screen	If the engine is down on power, check the screen in the muffler once the muffler has cooled. Clean it, or replace it if damaged or heavily carbonized.
Fuel	Use gasoline of at least 90 ROC. More than 10 percent alcohol can impair performance in engines with manually adjustable carburetors.
Chain still moves at idle	Have the saw checked and repaired by your servicing dealer.

If all of that is fine and the saw still will not hold a setting, the carburetor itself may be worn, which is a job for a Stihl dealer. A flooded engine is a different problem with a different fix, covered in our guide to starting a flooded Stihl chainsaw.

Limiter Caps, Adjustment Limits and When to See a Dealer

Many Stihl carburetors only let you move the screws a small distance. The MS 271 manual says “max. 3/4 turn” on H and “no further than the stop” on L. That limited range is deliberate: California’s small off-road engine regulation (CARB Title 13, Article 1) says engines are compliance-tested at any adjustable position within the range available to the end user, so makers restrict how far a screw can turn. Some saws also have plastic or metal caps over the H and L screws.

This guide does not cover removing limiter caps. If your saw has them, follow your model’s manual and let a Stihl dealer handle any work that needs the caps off. Stay inside the stops, and refer to your model manual or dealer for anything this chart does not cover.

Frequently Asked Questions

How do you adjust the H and L screws on a Stihl chainsaw?

First make the standard setting for your model from the owner’s manual, for example H counterclockwise to the stop (max. 3/4 turn) and L clockwise to the stop then 1/4 turn counterclockwise on the MS 271 and MS 291. Then set idle with LA. Touch H only for a small altitude correction, never beyond the stop.

What are the correct Stihl carb adjustment settings?

They depend on the model. The MS 170 and MS 180 use LD = 2 (idle screw only), the MS 210, 230 and 250 use H and L settings of 1 turn or H up to 3/4 and L 1 turn depending on the carburetor, and the MS 271 and MS 291 use H up to 3/4 turn and L 1/4 turn. Idle is 2,800 rpm in all of them. The MS 261 C-M has no manual setting.

How do you adjust the idle on a Stihl chainsaw?

Warm the engine up, then use the LA screw (LD on the MS 170 and MS 180). If the chain rotates, turn it counterclockwise until it stops, then a further 1/2, 1/4 or 1 turn depending on the model. If the engine stops, turn it clockwise until the chain begins to rotate, then back off by the same model amount.

What do H, L, and LA mean on a Stihl chainsaw carburetor?

H is the high-speed screw for full-throttle mixture, L is the low-speed screw for idle and low-throttle mixture, and LA is the idle speed screw that keeps the chain still at idle. On the MS 170 and MS 180 the idle screw is labeled LD.

Can running the H screw too lean damage a Stihl chainsaw?

Yes. Stihl’s manuals warn that a setting that is too lean increases the risk of engine damage through lack of lubrication and overheating, and that you should not make the mixture leaner to get an apparent increase in power.

Why can’t I adjust the carburetor on my Stihl chainsaw?

It may have limited screw travel or caps, or be an M-Tronic model such as the MS 261 C-M with no H or L screws. Check your manual, and refer to a Stihl dealer if the saw runs badly.

What is the high rpm setting on a Stihl chainsaw?

The manuals do not give a high-rpm number for the H screw. They list rated power, such as 3.5 hp at 9,500 rpm for the MS 271, and say H changes maximum off-load speed. Use the standard setting rather than adjusting for a higher top speed.