Small engine runs poorly: Common Causes & How to Fix
1Small Engine Carburetor Repair Kit
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 Repair Kit
- Remove air filter & carburetor. Take off air filter assembly. Detach fuel line and remove carburetor.
- Take apart carburetor. Remove bowl, gaskets, springs, needle valve and other interior components.
- Clean carburetor body. Spray all carburetor passages and channels with carburetor cleaner.
- Install new gaskets & seals. Replace gaskets, O-rings, needle valve and other seals with those from kit.
- Inspect other parts. Check floats, throttle lever, choke mechanism for wear or damage. Replace as needed.
- Reassemble carburetor. Install components in proper order and orientation per manufacturer's directions.
- Install carburetor on engine. Attach carburetor to intake manifold using new gaskets from kit. Reconnect fuel line.
- Replace air filter. Reattach air filter assembly over carburetor inlet.
- Test & tune engine. Start engine and adjust carburetor components to tune performance.
- Make sure to test at high and low RPMs, and adjust mixture settings as needed with repair kit components.
2Small 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.
3Small Engine Spark Plug
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.
4Small Engine Fuel Filter
Common Solution
Repair Instructions:
A clogged fuel filter can cause rough engine operation. Fuel filters get blocked from old gasoline left sitting in the tank. Over long periods, some fuel ingredients evaporate away. This leaves a thicker, stickier residue that clogs the filter. The restricted fuel flow prevents smooth running. Fix the issue by draining all old gas from the fuel tank. Add in fresh gasoline to refill the tank. Then replace the fuel filter completely. Follow the engine manual to remove and install the new filter properly. Allow some spillage during the process. Dispose of the old filter and fuel appropriately. Gasoline left unchanged for months can leave fuel deposits. Draining old gas and replacing filters clears blockages. Engines run smoother with clean filters and fresh fuel. Avoid future clogs by using fuel additives to stabilize gas in storage.
How to Replace a Small Engine Fuel Filter
- Locate fuel filter. The filter is typically inline along the fuel line running from the tank to carburetor.
- Disconnect fuel line. Use pliers to detach the fuel line from both ends of the old filter.
- Remove filter. Take out any retaining clips or brackets securing the old filter in place.
- Install new filter. Position the new filter in the same location as the old one using retaining clips if needed.
- Attach fuel lines. Connect the fuel lines to the corresponding inlet and outlet ends of the new filter.
- Check direction of fuel flow. Confirm fuel flows in the proper direction marked on the filter.
- Secure connections. Use zip ties or clamps to securely fasten the fuel lines onto the new filter.
- Check for leaks. Turn on fuel and check for leaks at the filter connections before starting engine.
- Start engine. Start the engine and inspect filter area to confirm no fuel leaks. Replace filter if leaks are present.