I'm about at my wits end with the POS Sthil FS36 that I was given my my Father in-law. I had a Ryboi Grass Scorpion 20 years ago and this is shades of that (also) POS.
Was using at full revs powering through the garden, and then it just stalled. It wouldn't re-start. I put more fuel in it (definitley 2-Stroke), tried choke, no choke, full throttle, no throttle, It just did not want to go. The first couple of tries, it started, but stalled again as soon as I went for full revs.
I'm going to try and pull it apart over the long weekend, but I'm almost ready to just scrap it and replace it - not going to spend any money on it (it is due a new line head also) but if I can pull it apart and it's an easy fix happy days.
These Stihl FS36 line trimmers have a Ryobi engine.
I think of mostly 3 problems with these engines not running.
1 Is the motor in good mechanical condition (good compression ,crank seals not leaking etc)
2 Is the ignition working properly ,( good spark ,correct timing)
3 Is the fuel system working correctly.(fresh Fuel ,correct ratio fuel mix , carby and filters working )
This trio resolves 95%+ of field issues on consumer trimmers, but rare extras like exhaust restrictions or electrical shorts (kill switch) can mimic these. Still, starting here avoids unnecessary disassembly.
If it will run on a little fuel down the spark plug hole or fuel sprayed into the carby throat ,that should tell you the coil or ignition is good.
If no signs of firing it could have a bad coil or shorting wires or the plug connector is bad or the motor is in bad mechanical condition.
I usually grab another spark plug to use in the trimmer I'm fixing,I would get a plug out of a running mower or line trimmer so I know if the old plug is the problem as they have a habit of breaking down when hot or under load.
First test the trimmer with a good known spark plug that is running in another trimmer or mower.
Before pulling a carby apart I always test the fuel filter ,primer and fuel hoses first , as a slightly blocked filter or a hairline crack in a fuel hose will stop the trimmer running and a bad primer can stop the engine running.
Temporary Fuel Supply Test for Line Trimmers This procedure describes how to test a line trimmer’s carburetor using an external primer bulb and a cup of fuel. The goal is to confirm whether fuel‑delivery problems are caused by the original fuel lines or in‑tank fuel filter, rather than by the carburetor itself. ​
1. Safety information Work in a well‑ventilated area away from flames, sparks, and hot surfaces.
Wear safety glasses and fuel‑resistant gloves.
Allow the trimmer engine and muffler to cool completely before starting work.
Use only fresh, correctly mixed 2‑stroke fuel in a clean container. ​
2. Required tools and materials Clean fuel hose (correct size for the carburetor and primer fittings)
Remote/in‑line primer bulb
Small glass jar or cup for fuel
Fresh 2‑stroke fuel mixture
Screwdriver and/or small pliers (for clamps and covers)
Shop towels or rags for spills
3. Preparing the trimmer Turn the trimmer OFF and move the stop switch to the OFF/STOP position.
Remove the spark plug cap to prevent accidental starting. ​
Place the trimmer on a stable, flat surface with the carburetor exposed and accessible.
Wipe away grass, dust, and debris from around the carburetor and fuel lines.
4. Disconnecting the original fuel supply Identify the fuel line that feeds fuel from the tank to the carburetor inlet nipple. On most trimmers, this is the line coming from the tank (or in‑tank filter) to the carb body. ​
Carefully pull this line off the carburetor inlet. Use pliers if a clamp is installed.
Inspect the visible portion of the line for cracks, splits, or hardening, but do not rely solely on visual inspection at this stage.
5. Setting up the temporary fuel and primer system Cut a length of clean fuel hose long enough to reach between the carburetor and your work area.
Push one end of this hose onto the carburetor fuel inlet nipple. Ensure it is fully seated.
Connect the free end of this hose to the OUT port of the primer bulb.
Attach another short length of fuel hose to the IN port of the primer bulb.
Place the free end of the hose from the IN port into a glass jar or cup filled with fresh 2‑stroke fuel. Ensure the hose end remains submerged in the fuel. ​
Note: In this configuration, the primer bulb will draw fuel from the cup on the IN side and push fuel toward the carburetor on the OUT side.
6. Priming and test running With the cup of fuel positioned safely and upright, squeeze the primer bulb several times.
Observe the fuel movement in the hoses:
Fuel should be drawn from the cup through the hose into the IN side of the bulb.
Fuel should then be pushed from the bulb’s OUT side hose into the carburetor inlet. ​
Continue priming until:
The hoses are full of fuel with minimal air bubbles.
The primer bulb becomes firm, indicating the system is charged.
Refit the spark plug cap securely.
Start the trimmer using the normal starting procedure (choke/half‑choke as per the manufacturer’s instructions). ​
Allow the engine to run and observe:
If the engine starts, idles, and accelerates cleanly while being supplied from the cup, the carburetor is receiving adequate fuel from this temporary system.
7. Interpreting test results 7.1 Engine runs correctly on temporary fuel supply If the engine runs normally using the jar‑and‑primer setup:
The carburetor is likely functioning correctly.
The fault is probably in the original fuel system, such as:
Split or cracked in‑tank fuel line
Split or cracked external fuel line
Blocked or heavily restricted in‑tank fuel filter
Kinked or collapsed line, or loose connections ​
In this case, proceed to Section 8 to repair or replace the original fuel components.
7.2 Engine will not run correctly on temporary fuel supply If the engine still fails to start, runs poorly, or dies even with this temporary fuel setup:
The problem may lie in:
Carburetor internal passages (blockages)
Damaged diaphragms or metering components
Ignition system issues (weak/no spark)
Low compression or mechanical wear ​
Further carburetor servicing, ignition testing, or engine diagnosis will be required.
8. Inspecting and repairing the original fuel system Empty the fuel tank or plug the opening to avoid spills.
Remove the fuel cap. Using a hooked wire or needle‑nose pliers, gently pull the in‑tank fuel filter and attached line out of the tank opening. ​
Inspect the in‑tank fuel line:
Look for splits, soft spots, brittleness, or sections that break easily.
Replace any damaged lines with new fuel‑rated hose of the correct size.
Inspect the fuel filter:
If the filter looks dirty, clogged, or very old, replace it with a new one of the same type. ​
Inspect the external fuel lines from tank to carburetor:
Check for cracks, hardness, or loose fittings.
Ensure there are no kinks and that routing is smooth.
Reinstall the new or inspected filter back into the tank and re‑route the lines to their correct carburetor connections.
Confirm all connections are tight and secure.
9. Final assembly and test Reconnect the trimmer’s original fuel line to the carburetor inlet.
Refill the fuel tank with fresh 2‑stroke mix.
Use the machine’s own primer bulb (if equipped) to purge air and draw fuel into the carburetor. ​
Refit the spark plug cap, if removed.
Start the engine following the standard starting procedure.
Verify:
The engine starts reliably.
It idles steadily.
It accelerates to full throttle without hesitation or stalling.
If the engine runs correctly now, the issue was likely a split line or blocked filter that has been corrected. If symptoms persist, proceed to full carburetor inspection and service according to the engine manufacturer’s service manual.
The books tell you to check the following.
What to check first
Fuel quality and mix: Even if you’re sure it’s 2-stroke mix, old or contaminated fuel can cause stalling or failure to restart. Drain the tank, clean or replace the fuel filter, and use fresh pre-mixed fuel at the correct oil ratio for a two-stroke engine. If you’ve got ethanol-blended fuel, it can cause issues over time; consider using a fuel stabilizer or ethanol-free fuel where available. ​
Spark plug and ignition: Remove the spark plug, inspect the electrode gap, and clean or replace if fouled. A weak or fouled plug can cause hard starting or stalling after a stumble, and a loose boot or bad ignition coil can also cause intermittent failures. Reconnect the boot firmly after checking. ​
Air intake and fuel delivery: Check the air filter for clogging and clean or replace if dirty. A clogged air filter or a plugged diaphragm/needle in the carburetor can cause rich/poor running and stalling when you throttle up. If you’re comfortable, inspect the carburetor for gummed passages and clean with approved carb cleaner. ​
Carburetor and fuel system: If fuel is getting to the carb but engine won’t stay running, the carburetor may be gummed up from old fuel. A common fix is a thorough carb clean or professional rebuild kit, particularly if the idle and high-speed circuits are out of balance. Ensure the primer bulb (if present) pulls and primes properly. ​
Fuel lines and vacuum: Inspect fuel lines for cracks, brittleness, or disconnections, especially if the line head is due to being replaced anyway. A pinched or air-leaking line will cause the engine to stall or run lean/fuel-starved at full throttle. Replace any damaged lines. ​
Exhaust and spark arrestor: A blocked exhaust or spark arrestor screen can cause poor running or stalling under load. Remove and inspect the exhaust opening; clean out carbon buildup if present. ​
Starter and choke procedure: If the engine starts briefly and stalls, ensure you’re using the correct choke procedure for cold starts. Some units need a few primer pumps or a specific choke position; if flooded, wait 20-30 minutes with the choke off to clear the excess fuel. ​
Observations and next steps
If it starts briefly but dies when you apply full revs, suspect carb or fuel delivery (fuel starvation, rich/lean imbalance, or a flooded condition). Try starting with a fresh fuel mix, then apply a short, gradual throttle rather than full throttle to see if it can settle into a stable idle before revving up. ​
If you recently used it hard with a strained load (tough grass, heavy weeds), the muffler or exhaust could be restricted or the air filter could be overwhelmed. Investigate for obvious blockages or debris in the air intake and exhaust. ​
If you can’t get it to run after the above checks, consider that a carb rebuild kit or a replacement carburetor is a common and cost-effective fix for stubborn FS36s, especially if the diaphragm or needle valve has deteriorated over time. ​
What to prepare if you dive in
Have basic tools: screwdrivers, pliers, a small socket set, a carb cleaning spray, and new spark plug(s) ready if you find fouling or corrosion.
Replacement consumables: fuel filter, air filter, fresh pre-mix fuel, and a carb rebuild kit for your model if you find internal carb components degraded.
Work plan: drain fuel, remove air filter cover, inspect spark plug, test ignition, check fuel lines and primer, then address carburetion step by step.
When to seek deeper help
If the unit still won’t run after cleaning and carb work, a professional carb rebuild or complete replacement of the carburetor is often the most reliable next step, especially on a machine you’re trying to avoid spending on. A reputable service can also check for compression issues that could cause stalling under load.
