Small engine wont start: Common Causes & How to Fix
1Small Engine Ignition Coil
Most Common Solution
Repair Instructions:
The ignition coil provides voltage to the spark plug to ignite the engine. If it's bad, the engine won't start. Before replacing it, check the spark plug first. Confirm it sparks properly when tested. If good, use an ignition coil tester tool. It checks coil operation. Clip tester lead clips to the coil output terminal and a ground. Crank the engine and check for tester sparking. No sparks indicate a failed coil. Replace any that don't pass the tester. Follow your manual for proper coil removal and installation. Bad coils prevent electric flow to the plugs. No sparks mean unburned fuel and no starts. Use coil testers to diagnose issues before replacing parts. Test coils and plugs separately to pinpoint failures. Replace defective coils to restore ignition and starting.
How to Replace a Small Engine Ignition Coil
- Disconnect spark plug wire. Remove the wire from the spark plug and ignition coil terminal.
- Remove mounting bolts. Take out any bolts or screws securing the ignition coil to the engine.
- Disconnect wiring. Detach the primary coil wire that runs to the magneto or points.
- Install new ignition coil. Position the new coil in the same location and orientation as the old one.
- Attach wires. Connect the primary coil wire to the proper magneto or points terminal.
- Secure ignition coil. Insert and tighten mounting bolts to secure coil in place. Avoid overtightening.
- Attach spark plug wire. Connect the spark plug wire to the ignition coil high tension terminal.
- Test operation. Start the engine and allow to run. Check that the ignition coil is firing properly.
- If issues occur, recheck all wiring connections and coil mounting. Make sure air gap is set correctly.
2Small Engine Spark Plug
Most Common Solution
Repair Instructions:
Check the spark plug for wear or damage. If the porcelain is cracked, the metal electrodes are burnt or worn down, or there's heavy carbon buildup, replace the plug. Use a spark tester tool to check if the plug is bad. Crank the engine while watching for a strong blue spark across the tester's gap. No spark means the plug needs replacing. A good spark plug should fire a sparking blue flash while cranking. Weak or no spark can cause starting issues or rough running. Worn or fouled spark plugs won't ignite the fuel mixture properly. Replacing damaged, carbon fouled, or worn out spark plugs can restore easy starting and smooth performance.
How to Replace a Small Engine Spark Plug
- Make sure the engine is cool before starting. Let the engine sit for at least 30 minutes after use before attempting to replace the spark plug. A hot engine can burn you.
- Disconnect the spark plug wire. Use a spark plug wrench to loosen the nut connecting the wire to the plug. Pull the wire off the plug.
- Clean around the base of the plug. Use a wire brush or scraping tool to remove dirt, oil or debris around the spark plug base. This allows you to access the plug easier.
- Remove the spark plug. Place the spark plug wrench or socket over the spark plug base. Turn it counterclockwise to unscrew it. Pull the spark plug out of the engine block.
- Inspect the spark plug. Check for excessive wear or buildup on the electrodes. Replace it if needed or clean it with a wire brush.
- Gap the new spark plug. Use a spark plug gap tool to set the space between the electrodes to 0.6-0.8 mm for most small engines. Refer to your engine manual for the proper gap size.
- Thread in the new plug by hand. Carefully thread the new or cleaned spark plug into the engine block by hand. This prevents cross-threading.
- Tighten with the wrench. Once seated by hand, use the wrench to tighten it another 1/8 to 1/4 turn. Don't over-tighten.
- Replace the spark plug wire. Push the wire back onto the spark plug and tighten the nut to secure it.
- Start the engine and test. Start the small engine and let it run to ensure the new spark plug is working properly.
3Small Engine Carburetor
Most Common Solution
Repair Instructions:
The carburetor can develop cracks from engine heat and vibration. Cracks allow fuel to leak out of the carburetor body. Check over the carburetor closely looking for any cracks or leaks. Also inspect for white corrosion powder which indicates cracks. If you see the carburetor body itself leaking fuel, it likely needs full replacement. Attempting to patch cracks rarely works, as the carburetor material is too damaged. Leaking fuel is extremely hazardous. Proper installation avoids leaks and safety risks. Never operate equipment with a leaking carburetor. Cracked carburetors that leak must be replaced, as fuel leaks have disastrous consequences. Replacing a faulty carburetor restores safe fuel system operation.
How to Replace a Small Engine Carburetor
- Disconnect the spark plug wire. Remove the wire from the spark plug so the engine doesn't accidentally start when working on it.
- Drain the gas tank. Use a siphon or pump to drain the gas from the fuel tank into an approved container. This reduces fire risk.
- Remove air filter cover. Take off the air filter housing and set aside to access the carburetor.
- Detach fuel line and throttle linkage. Use pliers to disconnect the fuel line from the carburetor inlet. Unhook the governor spring and throttle cable/rod from the carburetor.
- Remove carburetor. Take off clamp screw or nuts holding carburetor to manifold. Carefully pull carburetor away from engine.
- Clean mounting surfaces. Use carburetor cleaner and rag to wipe mating surfaces on the engine block and new carburetor.
- Install new carburetor. Place new carburetor against block, aligning holes. Reinstall clamp screw or nuts to secure in place.
- Reattach fuel line and throttle linkage. Connect fuel line back to carburetor inlet fitting. Reattach governor spring and throttle cable/rod.
- Reinstall air filter housing. Put air filter cover and housing back on, securing with clamps or screws.
- Reconnect spark plug wire. Push wire back onto spark plug and tighten nut.
- Test engine. Add gas to fuel tank. Start engine and let run, adjusting carburetor components as needed.
4Small Engine Flywheel Key
Common Solution
Repair Instructions:
A sheared flywheel key can cause engine issues. The small metal key piece connects the flywheel to the crankshaft. Sudden stops or backfires can break the key. This protects other engine parts from damage. But broken keys prevent proper flywheel spinning. Check for a broken key if the engine won't start or lacks power. Remove the flywheel to inspect the key. Follow your manual for safe removal steps. Look for a key snapped in half or missing from the shaft. Broken or missing keys need replacement with new properly sized keys. Install flies correctly with tight crank nut torque. Broken keys are a cheap, quick fix. Always replace sheared keys to restore smooth crankshaft and flywheel interaction. Prevent future shearing by fixing backfires and easing off throttle shifts.
How to Replace a Small Engine Flywheel Key
- Remove spark plug wire. Detach the spark plug wire from the spark plug to prevent accidental starting.
- Access flywheel. Take off any covers or guards blocking the flywheel. Remove debris buildup around flywheel.
- Extract flywheel nut. Use a socket wrench to turn the flywheel nut counterclockwise to remove it.
- Remove flywheel. Carefully pull the flywheel straight out to access the crankshaft and keyway.
- Take out old flywheel key. Use needlenose pliers to grasp and remove the damaged flywheel key from the keyway.
- Clean keyway. Use a wire brush or sandpaper to remove any burrs or debris from the keyway slot.
- Insert new flywheel key. Place new key into the crankshaft keyway. Tap gently if needed to fully seat it.
- Reinstall flywheel. Slide flywheel over crankshaft, aligning with the flywheel key.
- Replace and tighten flywheel nut. Thread flywheel nut back on and tighten with socket wrench.
- Reattach spark plug wire. Connect wire securely onto spark plug terminal.
5Small Engine Recoil Starter
Common Solution
Repair Instructions:
The recoil starter spins the engine to start it. Pulling the cord turns the pulley system and crankshaft. If the starter fails, the engine won't turn over. Remove it to inspect the spring, pulley, and ratcheting mechanism. Check that the tabs extend when pulling the cord. They should grab and rotate the hub. Releasing the rope should retract the tabs and rewind correctly. Repair any parts binding or sticking. Clean out dirt, oil, or debris in the starter. Lubricate springs and pulleys if squeaking. Replace any cracked plastic housings. Starters with damaged or worn parts need complete replacement. Follow your manual to remove and install them properly. This prevents over-tightening bolts or stripping threads. Recoil starters must spin freely to start engines. Repair or replace defective assemblies so pulling the cord turns over the motor.
How to Replace a Small Engine Recoil Starter
- Remove spark plug wire. Disconnect the spark plug wire from the spark plug to prevent accidental starting.
- Take out recoil bolts. Remove mounting bolts or screws securing recoil assembly to engine.
- Disconnect recoil rope. Unhook rope from pulley and carefully feed it out of starter.
- Extract recoil assembly. Carefully pull recoil starter unit away from engine to remove it.
- Install new recoil starter. Position new starter assembly over mounting holes in same orientation.
- Insert mounting bolts. Thread starter bolts in by hand first, then tighten with wrench. Do not overtighten.
- Attach recoil rope. Feed new rope through starter assembly and tie securely onto pulley.
- Wind rope. Grip starter handle and slowly wind the rope clockwise onto pulley until tight.
- Reconnect spark plug wire. Attach wire securely onto spark plug terminal.
- Test operation. Give rope a hard pull to confirm proper engagement. Start engine to test.
6Small Engine Safety Switch
Common Solution
Repair Instructions:
Use a multimeter to test the safety switch and see if it is broken. First, turn the power off for safety. Set the multimeter to test for continuity. This means checking if electricity can flow through the switch contacts. Touch the multimeter probes to the safety switch wires or terminals. Flip the switch on and off while testing. There should be continuity or a beep sound when the switch is in the on position. No beep means open contacts and a bad switch. The switch should show no continuity when turned off. This opens the circuit. If the switch does not act this way when tested, it is faulty and needs to be replaced. Follow wiring diagrams to test the correct switch for the appliance.
How to Replace a Small Engine Safety Switch
- Locate safety switch. Identify the safety switch on the equipment frame near a handle or foot pedal.
- Disconnect wires. Remove any plastic clips securing the switch wires. Label wires if needed.
- Unscrew switch Unthread switch mounting screws using a screwdriver. Remove switch.
- Position new switch. Place new safety switch in same spot. Insert and tighten mounting screws.
- Connect wires. Attach wires to corresponding terminals on new switch. Use plastic clips to secure.
- Test operation. Try starting the engine without activating the safety switch. It should not start.
- Start engine. Engage the safety switch by stepping on the foot pedal or grasping the handle. Start engine to confirm operation.
- If issues occur, recheck wire connections and switch orientation. Confirm switch closes circuit when activated.
- Replace switch if engine starts without switch activation or fails to start when activated.
7Small Engine Start Switch
Common Solution
Repair Instructions:
If the start switch sticks or works only sometimes, replacement is needed. Use a multimeter to test for switch continuity and confirm failure. Set the meter to ohms setting and touch probes to switch terminals. Check the 'on' and 'off' positions separately. The switch should show open contacts when turned on. Closed contacts in the off position complete the circuit. Any variance from proper readings means a defective switch. Follow the wiring diagram to test the right terminals. Ensure power is off for safety before testing. Compare results to a known good switch model too. Sticking or intermittent start switches hinder engine starting. Continuity testing diagnoses faulty switches for replacement. Match electrical ratings to original switch specifications.
How to Replace a Small Engine Start Switch
- Disconnect battery. Unhook the negative battery cable first to avoid shocks.
- Remove switch mounting nuts. Use wrenches to detach any nuts securing the switch to the engine frame.
- Disconnect wires. Label and remove the wires connected to the start switch terminals.
- Install new start switch. Position the new switch in the same spot and orient the terminals the same way.
- Connect wires. Attach the corresponding wires to the proper terminals on the new switch.
- Secure switch. Reinstall any mounting nuts and tighten with wrenches to secure switch in place.
- Insulate terminals. Cover wire terminals with electrical tape to prevent contact with metal.
- Reconnect battery. Reattach the negative battery cable first, then positive cable.
- Test operation. Turn key to ""Start"" position and listen for click of solenoid. Replace switch if needed.
- Start engine to confirm proper activation of starter.
8Small Engine On-Off Switch
Common Solution
Repair Instructions:
Use a multimeter to check if the on-off switch is broken and needs replacement. First, turn off the power supply for safety. Set the multimeter to test for continuity, meaning a complete electrical circuit. Touch the multimeter probes to the switch wires or terminals. Test it in both the on and off positions. The switch should show continuity only when flipped on. No beep or meter reading means open contacts in the off setting. This opens the circuit to turn off the appliance. If the switch does not conduct electricity when on or stays closed when off, it is faulty. Follow wiring diagrams to test the correct on-off switch.
How to Replace a Small Engine On/Off Switch
- Disconnect spark plug wire. Remove the spark plug wire from spark plug to prevent accidental starting.
- Disconnect wires. Remove any plastic clips securing the switch wires. Label wires if needed.
- Unscrew switch. Use a screwdriver to detach switch mounting screws or nuts to remove it.
- Install new switch. Position the new switch in the same location as the old one. Insert and tighten screws.
- Connect wires. Attach the corresponding wires to the proper terminals on the new switch. Use plastic clips to secure.
- Check operation. Flip the switch to ""On"" position. Use a multimeter to confirm power to the switch.
- Insulate terminals. Cover any exposed wire terminals with electrical tape.
- Reconnect spark plug wire. Attach wire securely onto spark plug terminal.
- Test engine. Flip switch to ""On"", pull the recoil starter. Engine should start and run. Turn switch to ""Off"" to stop engine.
- If issues occur, recheck all wire connections. Confirm switch activates/cuts power when toggled.
