STC American Lawn mower starts then stalls: Common Causes & How to Fix
1Lawn Mower Carburetor
Most Common Solution
Repair Instructions:
The carburetor might be plugged up. This usually happens if you leave gas sitting in the mower for a long time. Some stuff in the gas can evaporate over time, leaving a thick, sticky fuel behind. This sticky gas can clog up the carburetor and make the engine stall out. To fix a clogged carburetor, try cleaning it out with carburetor cleaner. If cleaning doesn't unclog it, you'll need to rebuild or replace the whole carburetor. Clogged carburetors are common when old gas sits in a mower. Using up or draining the gas tank regularly can help prevent the carburetor from getting gummed up with thick, sticky gas.
How to Replace Lawn Mower Carburetor
- Disconnect the spark plug wire - Locate the spark plug wire and detach it from the spark plug. This will prevent accidental starting while working.
- Drain the gas tank - Use a siphon or tip the mower to drain all gasoline from the fuel tank into an approved gas container. This minimizes spillage when removing the carburetor.
- Remove air filter - Take out the air filter housing and remove the air filter element. This allows access to the carburetor.
- Detach fuel line - Locate the fuel supply line attached to the carburetor inlet and disconnect it using pliers. Cap the end of the fuel line.
- Remove carburetor retaining nuts - Use a socket or wrench to loosen the carburetor retaining nuts attaching it to the engine intake manifold.
- Detach choke and throttle links - Remove any fasteners or rings connecting the choke and throttle controls from the carburetor levers.
- Lift off the old carburetor - Carefully lift the carburetor off of the intake manifold studs. Take care not to bend or damage linkages.
- Install new carburetor - Place the new carburetor onto the intake manifold studs. Reattach the choke, throttle, fuel line, air filter housing and retaining nuts.
- Reconnect spark plug wire - Attach the spark plug wire to the spark plug once done.
- Test operation - Add fresh gasoline to the fuel tank. Try starting the mower to ensure proper carburetor operation before fully reassembling. Make adjustments as needed.
2Lawn Mower Carburetor Repair Kit
Most Common Solution
Repair Instructions:
The carburetor might be plugged up. This usually happens if you leave gas sitting in the mower for a long time. Some stuff in the gas can evaporate over time, leaving a thick, sticky fuel behind. This sticky gas can clog up the carburetor and make the engine stall out. To fix a clogged carburetor, try cleaning it out with a carburetor cleaner. If cleaning doesn't unclog it, you'll need to rebuild or replace the whole carburetor. Clogged carburetors are common when old gas sits in a mower. Using up or draining the gas tank regularly can help prevent the carburetor from getting gummed up with thick, sticky gas.
How to Replace Lawn Mower Carburetor Repair Kit
- Remove air filter - Detach the air filter housing and remove the air filter element to access the carburetor.
- Drain fuel - Empty the gas from the fuel tank using a siphon or by tipping the mower. This reduces spillage when removing carburetor.
- Detach fuel line - Use pliers to disconnect the fuel supply line from the carburetor inlet. Cap the fuel line.
- Remove carburetor - Take out the retaining nuts and detach any choke/throttle links to fully remove the carburetor.
- Disassemble carburetor - Taking care to organize parts, fully disassemble the carburetor by removing gaskets, jets, float and needle.
- Clean carburetor parts - Use carburetor cleaner spray and small wire brushes to clean all removable parts and passages.
- Install new parts - Replace old gaskets, seals, and worn components with matching parts from the repair kit.
- Reassemble carburetor - Following proper assembly procedures, reinstall float, needle, jets, gaskets and other parts into the cleaned carburetor.
- Install carburetor - Mount the rebuilt carburetor back onto the engine and reconnect fuel line, air filter, choke/throttle links.
- Test operation - Add fresh gas to the fuel tank. Try starting the mower to ensure proper carburetor operation. Make adjustments as needed.
3Lawn Mower Fuel Cap
Most Common Solution
Repair Instructions:
The carburetor could be blocked up. This generally occurs if gasoline is left sitting in the mower for an extended period of time. Over time, some of the ingredients in the fuel may vaporize, leaving behind a thicker, stickier substance. This viscous fuel can obstruct the carburetor and cause the engine to die out. If the carburetor is congested, attempt cleansing it with carburetor cleanser. If cleaning the carburetor isn’t successful, rebuild or replace the entire carburetor. Clogged carburetors are prevalent when aged gasoline sits in a mower. Depleting or draining the gas tank regularly can help prevent the carburetor from becoming gummed up with thick, sticky gasoline.
How to Replace Lawn Mower Fuel Cap
- Disconnect spark plug wire - Locate the spark plug wire and detach it from the spark plug to prevent accidental starting.
- Drain fuel tank - Use a siphon to empty the gas tank into an approved fuel container. This prevents spills when removing old cap.
- Turn off fuel valve - If equipped, rotate fuel shut-off valve under the tank to the closed/off position.
- Remove old cap - Turn the old fuel cap counter-clockwise to unthread and remove it from the tank opening.
- Inspect o-ring - Check condition of sealing o-ring on old cap. Replace if worn or damaged.
- Install new cap - Align and hand thread the new fuel cap clockwise into the fuel tank filler neck.
- Tighten new cap - Once seated, continue tightening the new cap an additional 1/4 to 1/2 turn until snug. Do not overtighten.
- Add fuel to tank - Turn on fuel valve and pour fresh gasoline back into the empty fuel tank as needed.
- Reconnect spark plug - Reattach the spark plug wire to the spark plug once the new cap is installed.
- Check for leaks - Start mower and inspect new fuel cap for any leaks before fully reassembling. Reseat or replace cap if leaking.
4Lawn Mower Spark Plug
Most Common Solution
Repair Instructions:
Examine the STC American lawn mower's spark plug for wear or damage. Look for cracks in the porcelain insulator, burned or eroded electrodes, and heavy carbon deposits. If present, replace the plug. You can also check for a defective plug with a spark tester. While cranking the engine, a working plug will emit a strong spark between the tester terminals. No spark points to a bad plug needing replacement. Spark issues are usually due to a worn or fouled plug. Regular replacement every 100 hours ensures reliable ignition. Proper electrode gaps and tight plug seals are critical too. Inspect the spark plug wire and boot for cracking or looseness as well. Good connections ensure the plug receives full voltage to fire properly. With quality plugs, proper gaps, and secure wires, your mower's ignition will keep delivering strong sparks.
How to Replace Lawn Mower Spark Plug
- Disconnect the spark plug wire - Locate the spark plug wire, which runs from the spark plug to the magneto or electronic ignition module. Pull the boot off the end of the wire to disconnect it from the spark plug.
- Remove the old spark plug - Using the appropriate size spark plug socket or wrench, loosen the old spark plug by turning it counterclockwise. Once it is loose, unscrew it completely and pull it out of the engine.
- Inspect the old spark plug - Check the condition of the old spark plug. Look for signs of wear like erosion or buildup on the electrodes. This can help diagnose engine issues. Clean any dirt or debris from the spark plug threads.
- Gap the new spark plug - Use a spark plug gap tool to gap the new spark plug to the manufacturer's specified gap, usually between 0.020 and 0.060 inches. Adjust the side electrode to achieve the proper gap.
- Install the new spark plug - Carefully thread the new spark plug into the engine by hand until it is finger tight. Then use the socket or wrench to tighten it another 1/4 to 1/2 turn, being careful not to overtighten.
- Reconnect the spark plug wire - Push the boot back onto the end of the spark plug wire, connecting it securely to the top of the new spark plug.
- Start the engine and test - With the new spark plug installed, try to start the engine. If it starts up smoothly, the spark plug replacement was successful.
5Old or Bad Gasoline
Repair Instructions:
The STC American lawn mower's carburetor might be clogged. This common issue happens when you leave fuel in the mower for a long time. Over time, some fuel ingredients evaporate, leaving a thick, sticky substance. This gummy residue can clog the carburetor and stall the engine. To fix this, try cleaning the carburetor with a special cleaner. If that doesn't work, you may need to rebuild or replace the entire carburetor. Clogged carburetors are easily prevented by avoiding stale fuel. Use fuel stabilizer if storing gas over 30 days. Run the mower dry before storage to use up gas in the system. Check for sticky buildup and clean the carburetor yearly.
How to Replace Old or Bad Gasoline
- Disconnect spark plug wire - Locate the spark plug wire and detach it from the spark plug to prevent accidental starting.
- Drain old fuel - Siphon gas from the fuel tank into an approved container. Or tip the STC American lawn mower to pour out old fuel through the fill spout.
- Remove fuel filter - Locate the fuel filter along the supply line and use pliers to detach the fuel lines on both sides. Remove the old filter.
- Replace fuel filter - Attach new fuel filter to supply line with clamps, following direction of fuel flow.
- Flush fuel tank - Mix a fuel tank cleaning solution with some fresh gas in the empty tank. Shake vigorously, drain, and repeat until clean.
- Add new stabilizer - Pour fresh, clean unleaded gas back into the tank. Add fuel stabilizer to prolong shelf life.
- Reconnect spark plug - Reattach the spark plug wire to the spark plug once finished.
- Test mower - Attempt to start the mower to ensure fresh fuel flows through entire system. Check for leaks.
- Consider long-term storage - For mowers that won't be used for extended time, drain gas tank and run engine dry to prevent gumming.