Having to run your chainsaw with the choke knob pulled out to engage the choke indicates you have a problem that must be fixed for the best performance.
A SENIX chainsaw only runs with the choke on when the engine is getting too much air or not enough fuel.
This can be caused by a bad carburetor gasket, dirty carburetor, plugged fuel filter, clogged fuel vent, old gas, or a punctured or clogged fuel line.
Before making repairs, wait for all parts to stop moving and remove the spark plug wires.
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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.
SENIX Chainsaw Only Runs With the Choke On
Old fuel sitting in your chainsaw can be the root cause of many problems you begin to experience with your chainsaw.
Old gas sitting in a chainsaw can develop sticky substances and varnish that clogs fuel components and prevents a sufficient flow of fuel to the engine.
A reduced amount of fuel to the engine may require you to use the choke to reduce the amount of air getting to the engine. This is to correct the ratio of gas-to-air required for combustion.
Steps to take when you find old fuel in your 4-cycle chainsaw:
- Drain the tank.
- Prepare a fresh mix of gas with a fuel stabilizer in a fuel can. Use a product like Sea Foam or STA-BIL to assist with cleaning the fuel system and reducing moisture.
- Attach the fuel can cap and gently shake it to mix the additive with the gas.
- Fill the fuel tank with fresh fuel.
- Start the engine and allow it to run the saw for several minutes to work the fuel mixture through the fuel system.
Reduce the negative effects of fuel by following these tips:
- Use gasoline with a minimum octane rating of 87.
- Don’t use gasoline with an ethanol content greater than 10%.
- Use straight gas in a 4-cycle SENIX chainsaw. Don’t mix gas with oil for this type of engine.
- Store fuel in a dry location.
- Consume the fuel within 30 days before it begins to break down or add a fuel stabilizer to make it last a little longer.
Plugged Fuel Filter
A fuel filter’s function is to keep dirt and other contaminants out of the fuel system. You will find the fuel filter for your chainsaw inside the fuel tank.
It is a small cylinder-shaped part attached to the fuel line. When the filter isn’t changed regularly, it can become plugged with dirt. This will restrict the amount of fuel that is able to pass through the filter.
When there isn’t enough fuel to mix with air, you may have to run the chainsaw with the choke partly on to correct the ratio of air mixed with gas so the chainsaw continues to run.
Replace a plugged fuel filter:
- Replace the fuel filter by first taking a clean cloth and wiping around the fuel cap to prevent dirt from falling into the fuel tank.
- Remove the fuel cap.
- Tank note of the placement of the filter so you replace the new filter in the right position.
- Pull the fuel filter out of the tank. A clean bent wire or needle nose pliers work well for this.
- Remove the filter from the fuel line and insert a new filter.
- Place the filter inside the fuel tank in the correct position.
Punctured or Clogged Fuel Line
The choke may need to be on when the fuel line is clogged preventing a good fuel flow or air is being introduced to the fuel system through a puncture in the fuel line.
When the fuel line is clogged, the clog must be removed. To do this, remove the fuel line from the chainsaw.
Spray carburetor cleaner into the line to loosen the clog. Follow by blowing compressed air into the line to remove the clog.
Reinstall the line once the blockage has been removed. If you can’t open up the line or you find the fuel line is dry and cracked, you should replace it with a new one.
Look for a puncture in the line where air can be sucked into the fuel system providing additional air to the cylinder and making the choke necessary to correct the amount of air.
Plugged Fuel Vent
The fuel tank must be able to vent to allow air into the fuel tank as fuel is consumed. Without a vent, a vacuum will form keeping fuel from flowing out of the tank to the carburetor.
The vent on a SENIX chainsaw is in the fuel cap. If the vent hole is clogged, you can try to clean the cap to remove the clog or replace it with a new one.
You can test for a vacuum in the tank using a pressure gauge. If you don’t have one, follow the instructions below.
Quick test to determine if you have a bad fuel tank vent:
- Place your chainsaw on a level surface.
- Start the saw and remove the choke.
- If it begins to run sluggishly, loosen the fuel cap to allow air into the tank.
- If the engine begins to run well after allowing air into the tank, tighten the cap to try to replicate and confirm the problem.
- If the engine begins to run rough and act like it’s going to shut down, your fuel tank vent is most likely the problem.
- Replace the fuel cap.
Bad Carburetor Gasket
A carburetor gasket, located behind the carburetor, can deteriorate allowing air into the system because the gasket no longer seals correctly.
This causes a chainsaw to run lean when there is more air than fuel in the cylinder than the engine requires.
Access the carburetor and carefully remove the linkages and bolts attached to the carburetor. Remove the carburetor and gasket. Install a new carburetor gasket.
Before you install the carburetor, check it out. You may need to clean it while you have it off the chainsaw.
The carburetor’s function is to regulate the amount of fuel that is mixed with air to form combustion to start and run your chainsaw.
A buildup of varnish and deposits can make the carburetor unable to correctly perform this function.
If you are a little mechanical you should be able to handle cleaning your carburetor. Clean the carburetor by taking it apart and using the carburetor cleaner to remove deposits left behind from old fuel.
If the carburetor does not function after being cleaned, you may need to rebuild it or replace it with a new carburetor.
Carburetor Needs Adjustment
The carburetor may need to be adjusted to change the RPMs at idle speed and at full throttle. It may be causing the engine to run lean resulting in the need for the choke to be on.
SENIX recommends having an authorized service center make adjustments to the carburetor. Over-adjusting the carburetor can permanently damage the chainsaw and void any remaining warranty.
Contact SENIX with support questions on their website or by phone at 800-261-3981.