Even though you can keep your leaf blower running using the choke, you must find and fix the cause of the problem. It not only affects performance but also may cause additional damage if it is not repaired.
A STIHL leaf blower will only run with the choke on when it isn’t getting enough fuel or it is getting too much air.
A plugged fuel filter, old gas, dirty carburetor, fuel line puncture, bad carburetor gasket, or a plugged fuel vent can cause a STIHL blower to run with the choke on.
Shut off the blower and let the engine cool. Remove the spark plug boot before making repairs.
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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.
6 Reasons a STIHL Leaf Blower Only Runs With the Choke On
1. Old Gas
When your leaf blower isn’t getting a good flow of gas, old gas is often the underlying cause. This is because gas degrades and breaks down.
Fresh fuel must be consumed rather quickly. This is because gas begins to break down as quickly as 30 days after purchase.
Effects of Ethanol
The ethanol added to most gas sold today attracts moisture to the fuel system. Ethanol and water separate from the gas and leave behind varnish and gummy deposits causing fuel restrictions.
This mixture is also highly corrosive and may cause component failure affecting fuel getting to the engine.
Use a Fuel Stabilizer
Consume fuel within 30 days. If you are unable to use it this quickly, add a fuel stabilizer to make your fuel last a little longer before it breaks down.
Some 2-cycle oils include a fuel additive as well, but you need to confirm how long the additive is effective. Manufacturers may guarantee their fuel stabilizers last anywhere between 30 days and 2 years.
Type of Gas and Oil to Use in Your STIHL Leaf Blower
STIHL 2-cycle leaf blowers and 4-MIX leaf blowers require a fuel mixture of gas and oil at a 50:1 ratio. Use gasoline that has a minimum octane rating of 89 and a maximum ethanol content of 10%.
Ethanol is not good to run in your STIHL so don’t use fuels with higher ethanol contents than this.
Use a premium 2-cycle oil like STIHL High Performance or STIHL HP Ultra. Read more about choosing and caring for fuel used in your blower at This is the Gas and Oil STIHL Leaf Blowers Use.
SOLUTION: Remove old gasoline from your STIHL leaf blower. Add fresh fuel that includes an additive like Sea Foam or STA-BIL to stabilize the gas, clean the fuel system and reduce moisture.
2. Fuel Line Puncture or Clog
Air may get drawn into a cracked fuel line introducing air into the fuel system. A clog may have developed in the line reducing the amount of fuel moving through the fuel system.
The choke may have to be used to correct the fuel-to-air mixture if you find a punctured fuel line or a clog in the fuel line.
SOLUTION: Inspect the fuel lines for cracks or clogs. Replace any lines that are cracked. You can try to clean a clog using carburetor cleaner to loosen the clog and compressed air to dislodge it.
3. Plugged Fuel Filter
A fuel filter is used to keep dirt from entering the fuel system. It can restrict fuel flow when it isn’t changed regularly and becomes plugged with dirt and debris. I recommend replacing the filter annually to avoid running into this problem.
You will need to change it more often if you find your fuel is dirty. I highly advise against using old and dirty fuel. You may want to save a little money and not waste old fuel, however, in the long run, you may damage the carburetor or engine which costs you more money.
SOLUTION: Replace a plugged fuel filter. The filter is located inside the fuel tank. Wipe around the fuel tank cap before removing it to keep dirt from falling into the tank.
Take note of the location of the fuel filter so you can ensure you place the new filter in the same location. Pull the filter out of the tank. A clean bent wire works well to hook the fuel line to get to the filter.
Remove the old filter and attach a new fuel filter to the end of the fuel line and place it back inside the fuel tank. Reinstall the fuel cap.
4. Bad Carburetor Gasket
The gasket that sits behind the STIHL carburetor can deteriorate and become worse over time. When this happens, it no longer seals properly allowing additional air into the system causing it to run lean.
Running lean is when there is a higher concentration of air and less fuel than required by the engine. The choke will need to be on to compensate for the extra air being pulled into the engine through a bad carburetor gasket.
SOLUTION: Gain access to the carburetor and carefully remove the linkages and bolts attaching the carburetor. Remove the carburetor and gasket.
Reinstall a new gasket and reattach the carburetor, bolt, and linkages. Determine if you need to clean the carburetor since you have it off of the leaf blower.
5. Dirty Carburetor
The carburetor’s function is to regulate the amount of fuel that is mixed with air to form combustion to start and keep your STIHL leaf blower running.
Old gas that’s been sitting in your blower can leave a buildup of varnish and deposits that can negatively affect your carburetor.
It can clog the fuel jet reducing the amount of gas released into the cylinder.
SOLUTION: Clean the carburetor by taking it apart and using carburetor cleaner to remove deposits left behind from old fuel. If the carburetor doesn’t work after cleaning, you may need to rebuild it or replace it with a new carburetor.
A small engine mechanic at your local STIHL dealership or local small engine shop can assist you with this if you don’t want to tackle the task.
Plugged Fuel Tank Vent
A plugged fuel tank vent can reduce or prevent fuel from flowing out of the fuel tank. This is because a fuel tank needs to vent to equalize the air pressure. If it can’t vent properly it forms a vacuum.
A good indication you may have a fuel tank vent problem is when your leaf blower acts like it’s going to shut down and may need the choke to keep it running. However, when the fuel cap is loosened to allow air into the tank, the engine runs well without the choke on.
SOLUTION: Replace the fuel tank vent so air can flow into the fuel tank.