Stihl FS 36 Carburetor Settings (Tuning Guide)
For a Stihl FS 36, first identify the installed carburetor and check the matching manual; screw locations and settings can vary. On many versions, the LA screw controls idle speed. Adjust it in small steps only. Do not guess at H or L mixture settings: the wrong tune can damage the engine or make the cutting head unsafe.
A trimmer that starts, then dies when you release the throttle, can turn a quick yard job into a frustrating repair. It is tempting to turn every visible screw until the engine sounds better. On an FS 36, that can make the problem worse. A careful check of fuel, airflow, and idle behavior is safer than guessing.
I work through these symptoms in order: identify the carburetor, rule out basic faults, then adjust idle only if the evidence points there. The goal is a steady idle with the cutting attachment stopped, followed by clean acceleration and a stable return to idle.
Find the right carburetor settings for your FS 36
Carburetor settings are the adjustments that control engine speed and, on some carburetors, the fuel-and-air mix. FS 36 versions may use different carburetors, so there is no dependable screw-turn count for every machine. Use the manual that matches the trimmer’s model and serial details before changing any setting.
Look for the machine’s model and serial information, then inspect the carburetor for a maker’s name or model mark. The screws may be labeled LA, L, or H, but not every carburetor has the same layout or adjustment range. A screw’s position alone does not confirm its purpose.
| Marking | Usual purpose | Safe approach |
|---|---|---|
| LA | Sets idle speed on many FS 36 versions | Adjust in small steps if the engine will not idle or the head turns at idle |
| L | Low-speed fuel-and-air mixture, where fitted | Do not adjust without the exact carburetor procedure |
| H | High-speed fuel-and-air mixture, where fitted | Do not guess; use the specified procedure and a tachometer |
The idle speed is how fast the engine runs with the throttle released. A commonly listed FS 36 idle speed is about 2,800 rpm, but check your machine’s manual for its exact specification. Maximum engine speed also varies by engine and carburetor. Do not set it by ear or use a setting from an FS 36 chainsaw, another trimmer, or a different carburetor.
There is no universal “turn the screw out this far” baseline for all FS 36 carburetors. If your manual does not show a setting for the carburetor fitted to your machine, leave mixture screws alone and ask a qualified technician to identify the correct procedure.
Check the trimmer before adjusting idle
A carburetor adjustment will not fix a blocked filter, stale fuel, damaged fuel line, or other fault. Inspect the basic parts first, with the engine off and cool. Work outdoors, away from flames, sparks, and fuel vapors.
Use this check before starting:
- Fuel: Mix fresh unleaded gasoline at 50:1 with STIHL two-stroke oil, unless the manual for your exact machine or the oil maker’s instructions say otherwise. Do not use straight gasoline or assume a different oil has the same mixing ratio.
- Air filter: Check for dirt or damage. Clean or replace it as the manual directs; a clogged filter can affect engine running.
- Fuel system: Look for cracked or stiff fuel lines, leaks, or a damaged fuel filter. If your machine has a primer, check it for damage.
- Spark plug: Check the installed plug against the manual. Use the specified plug type and electrode gap, not a guessed substitute.
- Muffler and spark arrestor: Check for blockage or damage, and service them only as the manual allows.
- Controls and cutting parts: Confirm the throttle moves freely and returns when released. Check that the approved head, guard, and any required harness match the machine’s manual. Look for cracks, loose parts, or missing guards.
A fault in one of these parts can look like a carburetor problem. In my troubleshooting, I start with fuel and airflow because they are easy to overlook and can make a sound adjustment seem ineffective. If a line is deteriorated or a part is damaged, repair it rather than trying to tune around it.
Adjust the LA idle screw safely
The LA screw is an idle-speed adjustment on many FS 36 carburetors. It does not replace a proper mixture adjustment. Use it only after the basic inspection, and only if you have confirmed which screw is LA on your carburetor.
- Prepare the work area. Wear eye and face protection, hearing protection, gloves, long leg protection, and sturdy footwear. Keep people clear of the area where debris could be thrown. Set the trimmer on a stable surface, with the cutting attachment clear of people and objects.
- Start the engine as the manual directs. Use the correct cold-start steps. Once it starts, let it warm at operating speed before judging the idle. Keep the head pointed away from people and breakables.
- Observe the idle. Release the throttle and watch the cutting attachment from a safe position. The engine should idle steadily, and the attachment should remain still.
- Make a small LA adjustment. If the engine stalls at idle, turn LA clockwise a small amount. If the attachment rotates at idle, turn LA counterclockwise a small amount. Make one change at a time, then reassess the engine.
- Check the response. The engine should accelerate cleanly and return to a steady idle when you release the throttle. If the head keeps turning, the engine will not idle, or it surges, stop. Do not keep changing screws to force a result.
The correct adjustment is not simply “the engine stays running.” A safe idle also means the cutting attachment is stopped. If you cannot achieve both at once, the problem may need repair or carburetor service.
Diagnose common FS 36 running symptoms
A symptom can point to several causes, so use it to guide inspection rather than as proof that a screw needs turning. Stop the engine before checking the head, clearing tangled grass, or inspecting parts. If the engine races or surges at idle, stop using it until the cause is found.
| Symptom | Check first | Next step |
|---|---|---|
| Starts, then stalls at idle | Fresh fuel, air filter, fuel lines, and LA idle setting | Adjust LA slightly only if the basics check out |
| Cutting head turns at idle | LA setting and throttle return | Turn LA counterclockwise in small steps; stop if the engine then stalls |
| Hesitates or stalls under load | Fuel freshness, filter, fuel flow, air leaks, and muffler condition | Do not try to cure it with an arbitrary L or H adjustment |
| Surges or races at idle | Fuel restriction, air leak, blocked filter, or incorrect adjustment | Stop the engine; have the fault checked before further use |
| Runs poorly after storage | Old fuel, deteriorated lines, dirty filter, or a dirty carburetor | Replace damaged parts and use fresh, correctly mixed fuel |
A lean condition means the engine is getting too much air or too little fuel for the intended mix. Restricted fuel flow, an air leak, a blocked filter, stale fuel, or incorrect adjustment can contribute. A lean engine may race, lose power, or overheat before it seizes. Do not try to correct those signs by randomly opening or closing H or L screws.
Field examples: when idle adjustment is not the fix
These examples show a diagnostic approach, not a claim that every FS 36 has the same fault. The model’s exact manual and carburetor still determine the approved repair and adjustment.
Example 1: The head turns while the engine idles. After confirming the correct LA screw and checking that the throttle returns freely, make a small counterclockwise adjustment. If the head stops and the engine remains steady, recheck acceleration and return to idle. If the engine stalls before the head stops, stop the adjustment; a technician should inspect the cause.
Example 2: The trimmer races after sitting unused. Do not lower idle speed to mask a racing engine. Stop it and inspect for stale fuel, restricted fuel flow, damaged lines, or an air leak. A racing engine may be at risk of lean damage, and an arbitrary screw change can hide the symptom without fixing it.
Finish the job and store the FS 36
A correct idle setting is only one part of safe operation. Use only a cutting attachment approved for the exact FS 36 and guard setup. The FS 36 is a grass and weed trimmer, not a chainsaw or a brush cutter for woody material; do not use it for tree felling or unapproved attachments.
Keep the head below waist height and sweep it in a controlled motion, with the line parallel to the ground. Do not force it into dense growth. Stop the engine before removing wrapped grass, adjusting the head, or moving between work areas.
After trimming, let the engine cool before cleaning. Clear grass from the cutting attachment and air-intake area, inspect the head and guard for damage, and store the trimmer in a dry place with the attachment protected. Follow the manual’s fuel-storage directions. Before the next season, check fuel lines and the filter; replace deteriorated parts rather than tuning around them.
Frequently asked questions
These short answers cover the settings and symptoms FS 36 owners most often need to check. Use them as a starting point, not as a substitute for the manual that matches your carburetor and machine. If the engine races, overheats, or cannot idle safely, stop and seek service.
What is the correct idle speed for a Stihl FS 36?
About 2,800 rpm is a common FS 36 specification. Confirm the exact value in the manual for your model and serial details.
Which screw adjusts idle on an FS 36?
On many versions, the LA screw adjusts idle speed. Confirm its location and marking on your installed carburetor before turning it.
How many turns should the H and L screws be out?
There is no reliable setting that applies to every FS 36 carburetor. Use the exact carburetor procedure; do not guess.
Which way do I turn the LA screw if the engine stalls?
If the basic checks are sound, turn LA clockwise in a small step, then reassess idle.
What if the cutting head spins at idle?
Turn LA counterclockwise in a small step. If the head will not stop while the engine idles steadily, stop and have the trimmer checked.
What fuel mix does the FS 36 use?
Use fresh unleaded gasoline mixed 50:1 with STIHL two-stroke oil, unless the matching manual or oil instructions specify otherwise.
Can I use a chainsaw carburetor setting on my FS 36?
No. Do not apply settings from a chainsaw or another machine. The FS 36’s installed carburetor and matching manual govern its adjustment.
Why does my FS 36 surge or race at idle?
Possible causes include restricted fuel flow, an air leak, a blocked filter, stale fuel, or incorrect adjustment. Stop the engine and diagnose the cause instead of changing H or L at random.
Can I adjust the maximum engine speed by ear?
No. Use the maximum limit and procedure for the installed engine and carburetor, with a tachometer where required. A guessed high-speed setting can damage the engine.
What should I do if idle adjustment does not work?
Stop adjusting. Check the fuel, filter, lines, plug, muffler, and throttle return. If the trimmer still stalls, races, overheats, or spins its head at idle, have a qualified technician inspect it.
(This article was written by one of our staff writers, Harrison Croft. Visit our Meet the Team page.)
