A Bolens lawn mower won’t start due to a bad spark plug, plugged air filter, wrong choke setting, dirty carburetor, plugged fuel filter, sheared flywheel key, bad safety switch, or old gas.
Keep reading for additional reasons you may be running into a starting issue. Follow safety precautions including removing the spark plug boot(s) before completing any 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.
Bolens Mower Starting Problems (14 Causes & Solutions)
1. No Gas
A lack of fuel is an obvious reason why a Bolens mower won’t start. The small fuel tank on a Bolens mower requires you to refill it more often.
It’s easy to forget to check the tank level and run out of gas. It happens to the best of us.
SOLUTION: Fill and empty the tank with fresh unleaded gasoline with a minimum 87-octane. Choose a gas with an ethanol level no greater than 10%.
Most Bolens mowers being used use a 4-cycle engine that requires straight gasoline. However, a very old Bolens mower may have a 2-cycle engine that requires a gas and oil mixture.
A 2-cycle engine will only have one fill port for a gas and oil fuel mix.
2. Bad or Old Fuel
Gas can break down and begin to become less effective as soon as 30 days after purchase. Old gas can leave behind varnish and deposits that can clog the fuel system.
Your engine won’t start when it isn’t getting a good supply of gas.
Smell the gas or check its appearance to determine it’s bad. A pungent strong smell or a yellow darkened fuel are signs the fuel is bad. Compare the color of the fuel to some fresh fuel to identify the difference.
Use these tips when selecting gas for your mower:
- Use fresh gas with a minimum 87-octane rating and no more than 10% ethanol content for 4-cycle engines. Read more about choosing the right gas here.
- Consume fuel within 30 days.
- Store all fuel in a cool dry location to keep moisture out of the fuel.
- Use a fuel additive like Sea Foam Motor Treatment or STA-BIL to keep fuel stable for a little longer.
SOLUTION: Remove the old fuel from the fuel tank using a fuel siphon pump. Mix fresh fuel and a fuel treatment like Sea Form or STA-BIL to help clean the fuel system and stabilize the fuel. Add the fuel mixture to the fuel tank.
Once you are able to get your mower started, allow the engine to run for a while to allow the treated fuel mixture to work its way through the fuel system.
3. Bad Fuel Cap
A bad fuel cap with a clogged vent can keep the mower from starting. This is because the vent is used to allow air to pass through the tank cap.
The fuel tank will form a vacuum when the vent is clogged and the air is no longer able to get into the tank as fuel is consumed.
You can use a gauge to check for a vacuum. Don’t worry if you don’t have one. Another easy check is to loosen the cap to see if your engine will start once the air is allowed into the fuel tank.
If it does, confirm the cap is the problem by installing the cap, allowing the engine to run, and listening for the engine to begin to bog down and shut off.
SOLUTION: Replace a bad cap with a new one.
4. Bad Spark Plug or Loose Connection
The spark plug connection and spark plug can keep your mower from starting up. It is designed to ignite the compressed fuel and air mixture for combustion.
A fouled spark plug can cause the engine to misfire and not start.
SOLUTION: Check for a spark using a spark plug tester. If you aren’t getting a good spark, inspect the spark plug wire and spark plug condition.
- Remove the spark plug from the cylinder head and check its condition.
- If it is damaged, extremely dirty, or has burnt electrodes, you need to replace the plug.
- If it’s just a little dirty and in overall good condition, clean it with a wire brush. Be careful not to damage the metal.
- Check the gap and make sure it is to the manufacturer’s specifications.
- Install the good spark plug.
- Securely attach the spark plug wire so it makes a good connection.
5. Bad Ignition Coil
The ignition coil, also called an ignition module, provides voltage to the spark plug so it can fire and start the engine. A damaged coil can keep your mower from getting the spark it requires.
SOLUTION: After you verified your spark plug is in good condition, first inspect the condition of the ignition coil wire. If it is cracked, worn, or has exposed wires, you should replace the coil. Exposed wires can cause the coil to ground out and fail.
Next, check the continuity of your ignition coil. I like to use a spark tester to verify I am getting spark and the coil is working. You can also use a multimeter. Replace the ignition coil if you find a break in the continuity.
6. Sheared Flywheel Key & Timing Issue
A sheared flywheel key will cause the engine timing to be off so the spark isn’t created at the optimal time to ignite the fuel and air mix. This can affect starting.
Check these things that may indicate a sheared flywheel key problem:
- Inspect the mower blade. If the blade is damaged, the impact that caused the damage may have sheared the key. (Remove the spark plug wire when working with the blade).
- Pull the starter rope. A potential sheared key will cause the rope to spring back. It doesn’t allow for a smooth even pull.
SOLUTION: Replace the sheared flywheel key.
7. Clogged Air Filter
Air is required for your Bolens engine to run. If your air filter gets extremely dirty, it can starve the engine because sufficient air will no longer pass through the filter. A Bolen’s engine that doesn’t get sufficient air will not start.
When the airflow is blocked by the air filter the engine must find air to continue to run. It may begin to overheat and draw what air it can find from the crankcase which can cause extensive damage to the engine.
SOLUTION: Clean a paper air filter by removing it from the air filter housing. Take caution when removing it to ensure you are not dropping any loose dirt into the air intake.
You will need to wipe out any remaining dirt in the housing with a clean dry cloth.
Clean a PAPER air filter:
- Inspect the air filter for damage. The filter needs to make a good seal so air dirt doesn’t bypass the filter and get into the air intake. Replace a filter that is very dirty, damaged, or covered in fuel or oil. If it is a little dirty and in good condition, proceed with cleaning.
- Tap the filter against a solid surface to knock dirt out of the filter. Be careful to not damage the paper element.
- Install the filter and securely attach the air filter cover.
Clean a FOAM air filter:
*These are instructions for the primary foam filter. Never coat a foam pre-cleaner in oil. It can damage a paper air filter element.
- Inspect the foam filter for damage. Dry, brittle, or torn filters must be replaced. If the filter is in good condition, proceed with cleaning.
- Wash the filter in a bucket of water and mild dish soap to remove dirt.
- Rinse and allow the filter to completely dry. Sticking it out in the sun helps speed up the process.
- Lightly saturate the filter in clean engine oil. You don’t want the filter dripping with oil.
- Install the filter and attach the air filter cover.
You can find information on other types of air filters and how to clean them here.
8. Stuck Choke
The choke is used to regulate the amount of air pulled into the intake. The choke plate is closed to start a cold engine and open to start a warm engine. When the choke plate isn’t moved to the correct position, the mower won’t start.
A manual-choke model will have a throttle lever to open and close the choke. An auto-choke model will use a temperature gauge placed near the muffler to open and close the choke.
SOLUTION: Remove the air filter so you can see the choke plate. Verify the plate will open and close. If it doesn’t, loosen the stuck choke by lubricating any linkages and choke shaft with carburetor cleaner.
9. Clogged Fuel Filter
Your fuel filter is a line of defense to prevent dirt and debris from damaging the fuel system and engine by straining the fuel. The filter can become clogged when you’re running very dirty fuel or if it isn’t replaced regularly to keep it in good condition.
SOLUTION: Replace the fuel filter if you have found your fuel flow stops at the fuel filter.
If you don’t see the filter, you may have one installed at the bottom of the fuel tank. Shine a flashlight into the tank to look for the filter. If you find one, you’ll have to drain the fuel tank and then remove the fuel line from the fuel tank to access the filter.
Some engines will have a fuel strainer that sits at the top of the fuel tank and/or a fuel sediment bowl located under the fuel tank.
10. Clogged Fuel Line
Old fuel and dirt leave deposits that can clog your fuel line. This narrows or completly blocks the fuel passageway keeping a good flow of fuel from getting to the carburetor.
SOLUTION: Remove the fuel line, spray carburetor cleaner into the tube, and use compressed air to blow air through the tube until the line is free of dirt and gummy residue. You can also replace it with a new fuel line.
11. Clogged & Dirty Carburetor
The function of the carburetor is to regulate the right amount of gas with the right amount of air so your engine can create combustion. Carburetors can get crusty buildup and gummy deposits from using old fuel containing ethanol.
When the carburetor is no longer able to regulate the amount of fuel and air your engine receives, your Bolens engine will run rough or it may not even start at all.
SOLUTION: Remove the carburetor and clean it with a carburetor cleaner. Make sure the float bowl, float needle, and jet are working correctly. Replace a carburetor that is in poor condition or not working.
12. Bad Safety Switch
Your lawn mower uses a safety switch as part of the operator’s presence control system. The switch is designed to stop the engine when the operator lets go of the bail lever (the safety bar).
A faulty switch may not recognize when the bail lever is squeezed against the handle.
Check your operator’s manual for any additional safety switches that may be used on your model.
SOLUTION: Follow the cable from the bail lever down to the side of the engine to check if the switch is properly working. The switch is designed to ground when the lever is released.
Never use a mower with a bypassed safety switch.
Taking a guess at the problem and throwing parts at your mower can get pretty expensive.
13. Bad Starter Recoil
Bolens push mowers utilize a recoil to start the mower. The recoil can break and you are no longer able to start your mower.
SOLUTION: If the rope is no longer wrapped around your recoil, you may be able to restring it to get it working again. You may have a broken pulley, spring, or clips that need to be replaced.
If you find broken parts, you should price out the parts in addition to the whole recoil assembly. It may be more cost-effective to replace your recoil.
14. Poor Engine Compression
Poor compression will lead to a starting and running issue. It is an indication of an engine problem like head gasket, valve, cylinder wall, or piston ring damage.
A simple check you can do to tell if you are getting any compression is to remove the spark plug wire and slowly turn the blade backward to the compression stage. You should feel some resistance indicating there is some compression.
While this is a good initial quick check, it won’t tell you if you have sufficient engine compression. To check compression you’ll have to complete a compression test or a leak-down test.
Note: On engines with an automatic compression release (ACR), it’s best to do a leak-down test unless the manufacturer provides specifications for compression testing an ACR.