When the engine doesn’t run strong on your leaf blower and it’s running rough, it’s time to look for the reason sufficient air, fuel, or spark isn’t getting to the engine.
A STIHL leaf blower runs rough when the carburetor is dirty, the fuel filter is clogged, the fuel tank vent is plugged, the air filter is plugged, the spark plug is dirty, the fuel is old, or the spark arrestor is plugged.
Always shut off the blower, remove the spark plug boot, and wait for all parts to stop moving. Take care when working around the hot engine and muffler. It’s best to allow them to cool off to avoid injury.
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Follow all safety instructions provided in your equipment operator’s manual before diagnosing, repairing, or operating. Consult a professional if you don’t have the skills, or knowledge or are not in the condition to perform the repair safely.
8 Reasons Your STIHL Leaf Blower is Running Rough
1. Old or Bad Fuel
Gas doesn’t stay good forever. Actually, it doesn’t even stay good much longer than a month before it starts to break down.
When your leaf blower doesn’t start, runs sluggishly, or eventually stops running, the underlying problem is often old gas.
This is because most gas contains ethanol, an alternative fuel made from renewable resources like corn. This fuel naturally attracts moisture to the fuel system.
Ethanol and moisture are highly corrosive to the fuel system and engine. It will not only damage components but it will also leave behind varnish and gummy deposits restricting fuel.
Because of the negative effects of ethanol and old fuel, follow these tips when selecting fuel for your Stihl leaf blower:
- Purchase fresh gasoline and consume it within 30 days.
- Mix gas with 2-cycle engine oil at a 50:1 ratio in a separate container before adding it to the fuel tank.
- Gas must have a minimum 89-octane rating and a maximum 10% ethanol content.
- 2-cycle engine oil like these oils provided by STIHL: STIHL High Performance or STIHL HP Ultra
- Store gas in an air-tight container and away from moisture.
- Use a fuel additive to make fuel stable so it lasts a little longer.
STIHL 2-cycle leaf blowers require gas and oil mixed at a ratio of 50:1. 50 parts gas is mixed with 1 part oil. Refer to this guide on fuel for STIHL leaf blowers to get measurements to mix the fuel correctly.
STIHL 4-MIX leaf blowers: Stihl offers 4-stage leaf blowers designed to take advantage of the benefits of 4-cycle engines and still have the smaller format of a 2-cycle engine.
The 4-MIX engines use the same 50:1 fuel mix as the 2-cycle leaf blowers offered by STIHL.
2. Dirty Spark Plug
Spark is required to ignite the fuel and air mixture for combustion. A dirty or damaged plug can cause the spark plug to fire intermittently potentially causing the blower to run rough and sluggish.
In addition to a dirty spark plug, the electrode gap could be wrong or the spark plug wire could be loose resulting in poor engine performance.
Remove the spark plug using a spark plug wrench. Check its condition. Replace the spark plug if you find the tip is very dark in appearance, the porcelain is cracked or the electrode is burnt.
If you find your spark plug is just dirty, clean it with a wire brush or replace it with a new spark plug.
I prefer to use a new spark plug since it is a crucial component to having a leaf blower operating at its best. Make sure you have a properly gapped spark plug. You can check this using a feeler gauge.
Install the new or clean spark plug and securely attach the spark plug wire.
3. Plugged Fuel Filter
The fuel filter is used to strain fuel before it gets into the fuel system. This is to keep dirt from wearing the engine.
You will find the fuel filter attached to the fuel line and placed inside the fuel tank. When the filter isn’t replaced regularly, it can become plugged not allowing a good flow of fuel from getting to the carburetor.
A plugged STIHL fuel filter must be replaced:
- Set the leaf blower on a flat surface.
- Wipe around the fuel tank cap to remove dirt. Remove the cap.
- Take note as to where the fuel filter is located in the fuel tank so you place the new filter in the correct position.
- Pull the filter out of the fuel tank and remove the fuel line.
- Securely attach the new filter.
- Place the fuel filter back inside the fuel tank.
- Replace the fuel cap.
4. Clogged Fuel Line
Old fuel can clog the leaf blower’s fuel line restricting fuel flow. Look for a clogged line or a line that may have gotten pinched or kinked. Replace any damaged or clogged fuel line with a new fuel line.
5. Bad Fuel Tank Vent
The fuel tank vent can become plugged or damaged preventing air from passing through the vent to equalize the air pressure in the fuel tank. A plugged vent can cause a vacuum to form in the fuel tank. This keeps fuel from flowing out of the tank.
You can test this by loosening or removing the blower’s fuel cap to allow air into the tank. Start the blower, and allow it to run.
Be careful and keep your leaf blower level so you don’t spill any gas from the tank. If the blower runs strong and doesn’t bog down and run rough, tighten the fuel cap and see if you can replicate the issue to confirm the fuel tank vent is the problem.
Replace the fuel tank vent if your blower starts to act up and runs rough again after installing the fuel cap.
6. Plugged Air Filter
The engine requires air to run. Without enough air, the leaf blower will run sluggish and rough.
One of the items that can restrict airflow is a plugged air filter. The air filter can become plugged from dirt and debris when not regularly cleaned and changed.
If you find your air filter is plugged, I recommend replacing the filter. The small air filter is usually not very expensive. It is an important component when it comes to protecting the engine.
Because there are so many different types of filters used on a STIHL leaf blower, refer to your operator’s manual for steps to clean the style of air filter in your leaf blower.
Below I have listed cleaning instructions for a few common types of STIHL air filters.
- Clean a STIHL blower air filter:
- Move the choke to the on position to close the choke to keep dirt from falling into the carburetor throat.
- Remove the air filter cover and remove the air filter.
- Wipe out any dirt or debris remaining in the air filter cover or housing.
- Tap the filter against a solid surface or your hand to knock the dirt out of the filter.
- Install the clean filter. (Replace a very dirty filter or one that is damaged with a new air filter).
- Reattach the air filter cover.
7. Dirty Carburetor
The carburetor mixes the correct proportion of fuel with air for your leaf blower to perform at its best. The passageways can become clogged and the small components can fail to function correctly.
This can cause an insufficient amount of fuel mixed with air resulting in a rough running leaf blower.
You may be able to clean your carburetor to get it working again. You may end up having to rebuild (if rebuild kits are available for your carburetor) or replace the carburetor if cleaning doesn’t help.
8. Plugged Spark Arrestor
There is a small metal screen that keeps hot exhaust material from shooting out of the leaf blower causing injury or starting a fire. This screen is a spark arrestor.
It will become plugged with a carbon buildup that will affect how the engine runs when it isn’t kept clean.
Disconnect the spark plug wire. Remove the engine exhaust cover. Carefully remove the spark arrestor screen. Clean the screen with a metal brush and reinstall it. Reattach the engine exhaust cover. Reattach the spark plug wire.
If the screen isn’t able to be sufficiently cleaned or you find it is damaged or has a hole in it, replace it with a new spark arrestor screen.