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Small Engine Won't Start (Mower, Generator, Pressure Washer)

⚠️ Educational only — follow your service manual, use rated jack stands, and read our safety rules before you start.

The classic fuel–spark–air check for four-stroke small engines, plus carb cleaning basics.

Difficulty: Beginner · Time: 30–90 min ·

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Small Engines Fuel Engine Electrical Won't start Runs rough Surging / hunting idle

⚠️ Safety first

  • Disconnect the spark plug wire before touching the blade, carb, or anything that could turn the engine.
  • Work outdoors. Never run a generator or mower in a garage, shed, or near windows — CO kills.
  • Let the engine cool before refueling; drain fuel into an approved container away from flames.

Tools & supplies

🧰 Tools & parts needed / Recommended gear

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Steps

  1. Start simple: fuel in the tank, fuel valve on, choke set, safety bail/handle engaged, oil level correct (many engines have a low-oil shutdown).
  2. Check the fuel: gasoline older than ~30 days without stabilizer can gum up carbs. Drain and refill with fresh fuel.
  3. Pull and inspect the spark plug. Clean or replace, check the gap, and use a spark tester for a strong spark.
  4. Inspect the air filter; replace if clogged or oil-soaked.
  5. If it starts with a spray of starting fluid then dies, the carburetor is likely restricted. Remove the bowl, clean the jet with carb cleaner and a soft wire, and reassemble.
  6. Check for a clogged fuel filter or a pinched line, and that the tank vent cap isn't blocked.

🛑 When to call a pro

  • Engine has low compression or a bent crankshaft (after hitting something).
  • Generator output problems (wiring to a home requires a transfer switch and an electrician).

Printable checklist

WrenchReady — Small Engine Won't Start (Mower, Generator, Pressure Washer) · Date: ________ Vehicle: ________________

Video walkthroughs

Third-party videos embedded from YouTube; not produced or endorsed by us. Always follow your service manual.

Video thumbnail: Carburetor CleaningPlay video
Carburetor Cleaning — Champion Power Equipment. A manufacturer's own demonstration of cleaning a small-engine carburetor — the usual fix for a mower or generator that sat with old fuel.

FAQ

Can old gas stop a mower from starting?

Yes. Gasoline older than about 30 days without stabilizer can gum up the carburetor. Drain it into an approved container and refill with fresh fuel.

How do I know if the carburetor is the problem?

If the engine starts with a spray of starting fluid and then dies, the carburetor is likely restricted and may need cleaning.

Is it safe to run a generator in a garage?

No. Never run a generator or mower in a garage, shed or near windows — carbon monoxide can kill. Work outdoors.

Related guides

guide

No-Crank / No-Start Diagnosis

Turn the key and nothing happens (or just a click)? Work from the simple stuff to the starter in a logical order.

Beginner–Intermediate · 30–60 minguide

Outboard Motor Winterization

Protect a 2- or 4-stroke outboard over the off-season: fuel, flushing, fogging, gear oil, and storage.

Beginner–Intermediate · 1–2 hrs

References

Written by the WrenchReady team from general public knowledge. Specifications vary — your owner's/service manual is the authority.

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