Small Engine Repair: Common Problems and How to Fix Them

Small engines power much of the equipment we rely on every day, from lawn mowers and generators to pressure washers, golf carts, and UTVs. When these engines fail, the cause is often simple and inexpensive to fix. Understanding common small engine problems can save you time, money, and frustration. This guide covers the most frequent small engine repair issues and explains how to diagnose and fix them correctly.

Tools are linked throughout the blog for your convenience. I may earn a small commission on the featured links. You will not be charged extra for using the links.

How Small Engines Work (Quick Overview)

Every small engine needs three basic things to run:

Fuel

Spark

Compression

If any one of these is missing or weak, the engine will not start or run properly. Most small engine problems can be traced back to one of these systems.

1. Small Engine Won’t Start

Common Causes:

Old or contaminated fuel

Dirty carburetor

Fouled spark plug

Clogged air filter

Ignition coil failure

How to Fix It

Start with the basics. Drain old fuel and replace it with fresh gasoline. Check the spark plug and replace it if it’s dirty, worn, or oil-soaked. Inspect the air filter and clean or replace it as needed.

If the engine still won’t start, the carburetor is often the culprit. Ethanol fuel leaves varnish deposits that clog jets and fuel passages. Cleaning the carburetor thoroughly usually restores normal operation.

2. Engine Starts Then Dies

Common Causes:

Dirty carburetor

Restricted fuel flow

Blocked fuel cap vent

How to Fix It

If the engine starts briefly and then stalls, fuel delivery is usually the issue. Remove and clean the carburetor, paying close attention to the main jet and idle circuit. Check the fuel line for cracks or blockages.

Also inspect the fuel cap. A clogged vent can create a vacuum in the fuel tank, starving the engine of fuel. Try loosening the cap to see if the problem improves.

3. Engine Runs Rough or Surges

Common Causes:

Lean fuel mixture

Air leaks

Dirty carburetor

Partially clogged jet

How to Fix It

Surging or uneven running is a classic sign of carburetor problems. Clean the carburetor thoroughly and replace gaskets if needed. Inspect intake boots and gaskets for air leaks, which can cause a lean condition.

On adjustable carburetors, fine-tuning the mixture screws with these screwdrivers can help smooth out engine operation.

4. Lack of Power or Engine Bogging Down

Common Causes:

Dirty air filter

Fuel flow restriction

Worn spark plug

Low engine compression

How to Fix It

A clogged air filter restricts airflow and reduces power. Replace it if it’s dirty. Check the fuel system for restrictions, including the fuel filter and fuel lines.

If the engine still lacks power, perform a compression test. Low compression may indicate worn piston rings or valves, which require more advanced small engine repair.

5. No Spark from the Ignition System

Common Causes:

Faulty ignition coil

Kill switch or wiring issue

Incorrect coil air gap

How to Fix It

Remove the spark plug and test for spark. If there’s no spark, disconnect the kill wire from the ignition coil and test again. If spark returns, the problem is in the wiring or safety switch system.

If there is still no spark, the ignition coil may be faulty. Replace the coil and set the correct air gap according to manufacturer specifications.

6. Fuel Leaking from the Carburetor

Common Causes:

Stuck float

Worn needle valve

Damaged float bowl gasket

How to Fix It

Fuel leaks usually indicate a float or needle problem inside the carburetor. Disassemble the carburetor and inspect the float for damage or fuel inside it. Replace the needle valve and gasket if necessary.

Cleaning and rebuilding the carburetor often resolves fuel leakage issues.

7. Excessive Smoke from the Exhaust

Common Causes:

Overfilled crankcase

Incorrect oil type

Worn piston rings

How to Fix It

Check the oil level and drain excess oil if overfilled. Always use the manufacturer-recommended oil type.

If blue or white smoke continues, the engine may have internal wear. While this is less common, it may indicate worn rings or valve seals.

Preventing Future Small Engine Problems

Routine maintenance is the key to avoiding frequent repairs.

Maintenance Tips

Use fresh fuel and avoid storing ethanol gas

Add fuel stabilizer before long-term storage

Change oil regularly

Clean or replace air filters

Run the engine periodically during storage

These simple steps can significantly extend engine life and reduce the need for major repairs.

When to Repair vs Replace a Small Engine

Small engine repair is usually cost-effective, especially for fuel, ignition, and carburetor issues. However, engines with severe internal damage or extremely low compression may not be worth repairing.

If repair costs exceed 50% of replacement value, replacement may be the better option.

Final Thoughts

Most small engine repair problems are caused by fuel system issues, neglected maintenance, or simple wear items. By understanding how small engines work and knowing what to check first, you can fix many issues yourself and keep your equipment running reliably.

Whether you’re troubleshooting a lawn mower, generator, or outdoor power equipment, proper diagnostics and routine maintenance will save you time and money in the long run.