Whether you use a lawn mower, snow blower, pressure washer, or generator, small engines are the unsung heroes of home and yard care. But even the most reliable machines can develop issues—often at the worst possible time. The good news? Most small engine problems are easy to spot, understand, and often fix with some basic know-how. In this guide, we’ll walk through the most common small engine problems, explain why they happen, and offer straightforward troubleshooting tips so you can keep your equipment running smoothly all year round.
Quick Picks: The 5 Most Common Small Engine Problems
- Engine Won’t Start
- Engine Runs Rough or Stalls
- Smoke from Exhaust
- Loss of Power or Poor Performance
- Fuel or Oil Leaks
Why Small Engines Are Prone to Problems
Small engines work hard in tough conditions—exposed to dirt, dust, changing weather, and long periods of storage. Most issues are related to fuel, air, ignition, or basic maintenance. The good news is that modern engines are designed to be fairly easy to work on and many problems repeat across brands and models.
Detailed Troubleshooting: The Most Common Small Engine Issues
1. Engine Won’t Start
This is the number one complaint for mowers, trimmers, generators, and snow blowers. Before you panic, run through these checks:
- Old or Stale Fuel: Gasoline left in the tank for weeks or months can gum up carburetors. Always use fresh, clean fuel—add a stabilizer if storing for winter.
- Spark Plug Issues: Remove the spark plug—if it’s dirty, fouled, or corroded, clean or replace it. No spark? Try a new plug first.
- Choke and Primer: Double check that you’ve set the choke (cold engine) and primed as needed for your model.
- Fuel Shutoff Valve: Make sure it’s open. Some owners forget after last season’s shutdown.
- Air Filter: A clogged air filter starves the engine of oxygen. Pop it out and replace or clean as needed.
- Dead Battery (Electric Start): If your small engine has electric start, a weak or dead battery is common after storage. Jump or recharge it.
Quick Fix: Replace the fuel with fresh gas, install a new spark plug, and clean/replace the air filter for a fast, reliable start.
2. Engine Runs Rough, Surges, or Stalls
Is your mower revving up and down, sputtering, or quitting after a few minutes? The main causes are:
- Dirty Carburetor: Old gas gums up carb jets—try using a carburetor cleaner spray or, for stubborn cases, a rebuild kit.
- Vacuum Leaks: Torn gaskets or loose carburetor bolts allow extra air in, causing surging. Check for loose parts or visible cracks.
- Clogged Air Filter: If the filter is dirty, replace it—never run without a filter.
- Fuel Line Issues: Kinks or cracks can cause stalling—replace old or brittle hoses.
- Water in Gas: If condensation gets into the tank, the engine may surge or stall. Drain and refill with fresh fuel.
Tip: Consistent, rough running is almost always air/fuel related—start with a fresh filter and carburetor cleaning.
3. Excessive Smoke from Exhaust
Not all engine smoke is bad, but colored smoke usually means something is wrong:
- White Smoke: Often caused by overfilled oil or oil leaking into the combustion chamber (tipped mower or blown head gasket).
- Black Smoke: Too much fuel or too little air—usually a dirty air filter or carburetor running too rich.
- Blue Smoke: Oil is burning—likely due to worn piston rings, seals, or running at too steep an angle.
Fix: Check oil level, replace the air filter, and make sure you’re operating on flat ground. If smoke persists, consult a service shop.
4. Loss of Power or Poor Performance
If your mower, tiller, or trimmer isn’t cutting like it used to, there’s usually a simple explanation:
- Dull Blade or Chain: Sharpen blades or replace chains for better cutting and less strain on the engine.
- Dirty Air Filter: Replace it—engines need air to make power.
- Old Fuel: Fresh gas improves power and performance instantly.
- Clogged Fuel Filter: Replace as part of your seasonal tune-up.
- Valve Issues: Engines with lots of hours may need valve adjustments—check your manual or ask a shop.
Tip: Regular maintenance—especially blades and air filters—prevents most power loss problems.
5. Fuel or Oil Leaks
Leaks aren’t just messy—they can be a fire hazard. If you notice a puddle or strong smell, check:
- Cracked Fuel Lines: Replace old rubber lines every few years.
- Loose Drain Plugs or Fittings: Hand-tighten, but don’t overtighten and strip the threads.
- Worn Gaskets: Replace if you see oil or fuel seeping at the seams or under the engine.
- Carburetor Overflow: If the carb leaks after shutdown, the float may be stuck—clean or rebuild the carburetor.
Prevention: Annual checks for hoses, gaskets, and fasteners can catch leaks early and save major repairs.
Comparison Table: Quick Troubleshooting at a Glance
| Problem | Likely Cause | Quick Fix |
|---|---|---|
| Won’t Start | Old fuel, spark plug, air filter | Fresh gas, new plug, clean filter |
| Runs Rough/Surges | Dirty carb, air leak, clogged filter | Clean carb, replace gasket/filter |
| Smoke | Overfilled oil, dirty air filter | Check oil, replace air filter |
| Poor Power | Dull blades, old gas, filter | Sharpen blades, new gas/filter |
| Leaks | Cracked lines, gaskets, carb | Replace lines, gaskets, service carb |
FAQ: Small Engine Troubleshooting
Why won’t my mower start after winter storage?
The most common reasons are stale fuel, a dead battery, or a fouled spark plug. Drain old gas, charge the battery, and replace the spark plug for best results.
Is it safe to clean a carburetor myself?
For most homeowners, basic carb cleaning with a spray cleaner is safe. For full disassembly and rebuilds, follow your manual or visit a repair shop.
What fuel should I use in my small engine?
Always use fresh, unleaded gasoline (87 octane or higher) with no more than 10% ethanol. For 2-cycle engines, mix oil and gas as specified in your manual.
How often should I change my air filter and spark plug?
Most experts recommend checking every 25 hours of use, and replacing every season or at least every 50 hours.
How can I prevent small engine problems?
Perform regular maintenance: change the oil, keep fuel fresh, replace filters and plugs, and store your equipment properly over the off-season.
Pro Tips for Small Engine Care
- Keep fuel fresh—never leave old gas in the tank for months.
- Sharpen and balance blades to reduce engine stress.
- Check and tighten bolts and screws to prevent vibration issues.
- Clean the engine and cooling fins to avoid overheating.
- Read your owner’s manual—every engine has specific maintenance needs.
Conclusion & Call to Action
Most common small engine problems can be prevented or fixed with a little care and attention. Don’t let a hard-starting mower or sputtering snow blower ruin your weekend. With the tips and troubleshooting steps above, you’ll be ready for smooth starts and strong performance all year. For bigger repairs, your local service center or small engine dealer is there to help—don’t wait until the busy season to get your equipment checked!