Bolens Lawn Mower Will Not Start: Quick Fixes & Full Troubleshooting – 2025

Nothing’s more frustrating than gearing up to mow only to find your Bolens lawn mower will not start. The quickest fix in many cases is simple: check the fuel, spark plug, and air filter. Replace old gas, reseat the spark plug wire, and clean or replace the air filter—these steps often revive a stubborn mower in minutes.

In this complete guide, you’ll get a step-by-step troubleshooting plan for walk-behind and riding Bolens mowers. We’ll cover the most common causes, easy fixes, deeper diagnostics (carburetor, safety switches, starter systems), prevention tips, when to call a pro, and FAQs. By the end, you’ll know exactly how to get your Bolens running reliably again.

Common Causes of a Bolens Lawn Mower Not Starting

• Stale or contaminated fuel (more than 30–60 days old)
• Clogged carburetor or jets from varnished fuel
• Dirty or soaked air filter restricting air intake
• Faulty, fouled, or incorrectly gapped spark plug
• Safety switch not engaged (blade/seat/handle controls)
• Flooded engine (strong fuel smell, wet plug)
• Bad fuel shutoff valve or clogged fuel filter/lines
• Low compression due to stuck valves (less common)
• Dead battery, blown fuse, bad starter solenoid (riding mowers)
• Sheared flywheel key after a sudden blade impact

How to Fix a Bolens Lawn Mower That Won’t Start

Before you begin:
– Important: Disconnect the spark plug wire before working on the engine. For riding mowers, remove the key and disconnect the negative battery cable.
– Tools that help: socket set, spark plug wrench, carb cleaner, fresh gasoline (E10 or less), fuel stabilizer, small brush, multimeter (for battery checks), starting fluid (for diagnostics only), feeler gauge (for spark gap).

Method 1: Quick Start Checks (Fast Wins)

Diagnosing the Issue

• Time: 10–20 minutes
• Best for: First-time no-start symptoms after storage or sporadic use.

Fix Steps

1. Check fuel quality
   – If gas is older than 60 days, drain the tank and carb bowl. Refill with fresh fuel. Add fuel stabilizer if desired.
   – Inspect for water or debris in the tank.

2. Inspect and reseat the spark plug
   – Pull the spark boot off and push it back on firmly.
   – Remove the plug using a spark plug socket. If it’s black, wet, or corroded, clean or replace it.
   – Typical small engine plug: Champion RJ19LM/J19LM or equivalent (consult your Bolens model manual). Gap usually 0.025–0.030 inches.

3. Clean the air filter
   – Foam filter: wash with warm soapy water, dry completely, lightly oil, squeeze out excess.
   – Paper filter: tap gently to clear debris; replace if heavily soiled.

4. Verify safety controls
   – Walk-behind: hold the bail/handlebar safety lever fully against the handle.
   – Riding: sit on seat, brake engaged, PTO/blade switch off, gear in neutral.
   – Ensure the blade control cable isn’t slack or broken.

5. Prime and start properly
   – Press primer bulb 3–5 times (if equipped).
   – Set choke as directed by your model (full choke when cold).
   – Pull the cord firmly or turn the key for 3–5 seconds. Avoid repeated rapid pulls to prevent flooding.

Testing

• If the engine fires or runs briefly, you likely had stale fuel, poor spark, or air restriction. If it still won’t start, move to Method 2.

Method 2: Fuel System and Carburetor Troubleshooting

Diagnosing the Issue

• Time: 30–90 minutes
• Symptoms: Starts and dies, no start with fuel smell, primer bulb not filling, surging.

Fix Steps

1. Verify fuel flow
   – Open the fuel cap—listen for a hiss (vacuum). A clogged cap vent can starve fuel; try starting with cap loosened briefly.
   – Check the fuel shutoff valve (if equipped) is ON.
   – Pull the fuel line at the carb inlet and briefly open the valve. Fuel should flow steadily into a container. If not, replace the fuel filter and clear/replace the fuel line.

2. Clean the carburetor bowl and jet
   – Remove the carburetor bowl (usually a 10mm bolt). Expect some fuel; use a catch pan.
   – Clean the bowl and bolt thoroughly. Many bowl bolts contain a tiny jet/orifice—clear it with carb cleaner and a soft wire strand.
   – Reinstall with a new bowl gasket if damaged.

3. Full carburetor cleaning (if needed)
   – Remove the carburetor: detach the air filter housing, linkages, and fuel line.
   – Disassemble float, needle, main jet, and emulsion tube.
   – Soak metal parts in carb cleaner; blow out passages with compressed air. Do not damage soft rubber or plastic parts.
   – Reassemble carefully, ensuring the float moves freely and the needle seats.

4. Fuel quality and additives
   – Use fresh gasoline (E10 or less). Avoid fuel with high ethanol content.
   – Consider adding a carb cleaner additive on reassembly to prevent varnish.

Testing

• Prime and start. If it runs strong, the fuel path and carb are resolved.
• If it only runs on choke, the main jet may still be restricted—repeat cleaning or replace the carburetor.

Method 3: Spark and Ignition System Checks

Diagnosing the Issue

• Time: 15–40 minutes
• Symptoms: No fire even with starting fluid, plug is dry, repeated flooding, backfires.

Fix Steps

1. Spark plug test
   – Use an in-line spark tester or ground the plug’s metal threads to the engine and pull the rope. Look for a strong blue spark.
   – Replace the plug if spark is weak or absent. Confirm correct gap (0.025–0.030″).

2. Inspect the ignition coil (armature)
   – If no spark with a known-good plug, disconnect the coil kill wire and test again. If spark returns, a safety switch or wire is grounding the coil.
   – Check coil-to-flywheel air gap (commonly 0.010–0.014″). Adjust using a business card as a spacer if needed.
   – Replace the coil if still no spark.

3. Check the flywheel key
   – If you hit a rock/root recently and now have hard starting or backfiring, the flywheel key may be sheared.
   – Remove the flywheel nut and inspect the key. Replace if damaged and torque the nut to spec per your engine model.

Testing

• Spray a small amount of starting fluid into the intake and crank. If it fires briefly, spark is present and fuel delivery is suspect. If no fire, revisit ignition and safety circuits.

Method 4: Safety Switches, Cables, and Starting System (Riding Mowers)

Diagnosing the Issue

• Time: 20–60 minutes
• Symptoms: No crank with key, clicking solenoid, intermittent start, shuts off when engaging blades.

Fix Steps

1. Battery and cables
   – Charge and test battery: 12.6V+ at rest; drops no lower than ~10.5V during crank.
   – Clean and tighten terminals. Replace corroded cables.

2. Fuses and ignition switch
   – Check for a blown fuse near the battery or harness; replace with same rating.
   – Wiggle-test the ignition switch; replace if intermittent.

3. Safety interlocks
   – Seat switch: must be depressed while starting and running with blades engaged.
   – Brake switch: pedal fully down to start.
   – PTO switch: must be OFF to start.
   – Test continuity with a multimeter; replace faulty switches.

4. Starter solenoid and motor
   – If you hear a click but no crank, jump the solenoid posts briefly with an insulated tool to test the starter motor. If the motor spins, replace the solenoid; if not, test/replace the starter.
   – Warning: Only perform jumping if you are comfortable and follow safety precautions.

Testing

• After repairs, confirm proper cranking and running with all safety switches functioning.

Method 5: Air, Compression, and Mechanical Checks

Diagnosing the Issue

• Time: 20–60 minutes
• Symptoms: Pull cord very easy (low compression), mower starts then stalls under load, loud popping.

Fix Steps

1. Air filter and intake leaks
   – Ensure the air filter is clean and the housing seals are intact to avoid lean conditions.

2. Compression check
   – Use a small-engine compression gauge. Healthy engines typically exceed ~60–90 psi with compression release (varies by model). Very low readings suggest valve or ring issues.

3. Valves and lash (advanced)
   – On OHV engines, remove the valve cover and check valve lash. Adjust to engine spec if out of tolerance. Sticky valves may require cleaning or head service.

4. Exhaust blockage
   – Check for clogged spark arrestor screen in the muffler; clean or replace.

Testing

• If compression and airflow are restored, the engine should start and run smoothly.

How to Prevent Future Starting Issues

• Use fresh fuel and add stabilizer if storing more than 30 days.
• Run the engine dry or shut off fuel and drain the carb bowl before winter storage.
• Replace the spark plug every season or every 100 hours.
• Clean/replace the air filter regularly; more often in dusty conditions.
• Change engine oil at least annually (after the first 5 hours on new engines).
• Keep the deck clean to avoid impacts that shear the flywheel key.
• Maintain cables and safety switches; lube as needed and check operation.

Pro Tips

• Prime smarter: Over-priming floods engines. If flooded, open choke, hold throttle wide open (if equipped), and pull 5–6 times or remove and dry the plug.
• Use non-ethanol fuel where possible; ethanol attracts moisture and gums carbs.
• Replace the carburetor if repeated cleanings fail. Aftermarket carbs for common Bolens/MTD/Briggs engines are inexpensive and fast to install.
• Keep a spare spark plug and air filter on hand—cheap parts solve many no-starts.
• Inspect the blade and key after any sudden stop; replace both if the blade is bent and the key is sheared.
• Store indoors or use a cover; moisture corrodes electricals and contaminates fuel.
• Label fuel cans with date purchased so you don’t accidentally use stale gas.

When to Call a Professional

• You have no spark after replacing the plug and testing the coil/kill circuit.
• The engine has very low compression or noisy internals (knocking, grinding).
• Flywheel, crankshaft, or internal valve work is required.
• Electrical diagnosis on riding mowers is beyond your comfort level.
• Carburetor rebuilds on newer emissions models with tamper caps.

Typical costs:
– Carburetor replacement: $50–$150 parts and labor
– Ignition coil: $75–$150
– Starter/solenoid service (riding): $100–$250
– Full tune-up (plug, air filter, oil, blade sharpen): $80–$180

Warranty notes:
– Check your Bolens/MTD warranty terms; self-service may not void warranty, but modified parts or incorrect repairs can. Keep receipts and document maintenance.

FAQ

Q: My Bolens mower starts, then dies after a few seconds. What’s wrong?

A: This often points to a clogged carburetor main jet or restricted fuel cap vent. Loosen the cap to test venting. If it still stalls, clean the carb bowl and jet, or replace the carb.

Q: Which spark plug does my Bolens walk-behind use?

A: Many Bolens/MTD push mowers with Briggs & Stratton engines use Champion RJ19LM or equivalent, gapped to 0.025–0.030 inches. Always confirm with your engine model number stamped on the blower housing.

Q: How do I know if my engine is flooded?

A: You’ll smell fuel, the spark plug will be wet, and pulls get easier with no ignition. Dry the plug, open the choke, and pull with throttle wide open (if equipped) to clear excess fuel.

Q: My riding mower only clicks when I turn the key. Fix?

A: Check battery voltage, terminals, and ground. If the battery is good (12.6V+), test the solenoid. A single click typically means low voltage, bad connection, or failed solenoid.

Q: Can bad gas really stop a mower from starting?

A: Yes. Gasoline degrades in 30–60 days. Ethanol fuels absorb water and form varnish, clogging jets. Always use fresh fuel and a stabilizer for storage.

Q: The pull cord is very easy to pull and there’s no start. Why?

A: Likely low compression due to stuck valves, blown head gasket, or a sheared flywheel key throwing off timing. Perform a compression test and inspect the flywheel key.

Q: My mower only runs on choke. What does that mean?

A: The engine is running lean—usually a clogged main jet or air leak. Clean the carburetor and check gaskets and intake boots.

Alternative Solutions

If repeated repairs fail or the mower is older with multiple issues, consider these options:

Get Your Bolens Mower Working Again

Following this guide, you now have multiple solutions to fix a Bolens lawn mower that will not start:
– Quick checks: fresh fuel, spark plug, and air filter
– Fuel system and carburetor cleaning or replacement
– Ignition and flywheel key inspection
– Safety switches, battery, and starter system diagnosis (riding mowers)
– Preventive maintenance to avoid future no-starts

Don’t let a no-start ruin your mowing day. Start with the simple steps, work methodically, and you’ll usually have your Bolens running in under an hour.

Have you successfully fixed your Bolens? Share your experience or specific model in the comments so we can help others with targeted advice. Found this helpful? Bookmark it for your next tune-up and keep your Bolens starting on the first pull.