Why the spark plug on the gas trimmer floods and how to fix it: a complete guide

You pulled the starter cord and the trimmer didn't even sneeze - just the smell of gasoline and a wet spark plug? This problem is familiar to every second owner of power tools. Flooded spark plug - one of the most common reasons why the trimmer does not start when cold or after a long period of inactivity. But in 90% of cases it can be fixed on your own in 10-15 minutes, without contacting service.

In this article we will look at physical reasons flooding of spark plugs (from incorrect starting to carburetor malfunctions), we will give step by step instructions on drying and cleaning, and also tell you how to prevent the problem from recurring. We will pay special attention hidden defects that disguise themselves as a “filled candle” - for example, air leaks through the gasket or wear of the piston group. If your Husqvarna 128R, Stihl FS 55 or Patriot PT 555 stubbornly refuses to start - read on.

Why the spark plug on the trimmer floods: 7 main reasons

Plug flooding occurs when too much fuel enters the combustion chamber and there is not enough spark to ignite it. Gasoline literally “floods” the electrodes, making it impossible for a discharge to form. Here are the key reasons:

• 🔧 Incorrect startup algorithm. Most often, the spark plug is flooded due to excessive pressure on the primer (suction) or repeated unsuccessful pulls of the starter.
• ⚙️ Unadjusted carburetor. A rich fuel mixture (excess gasoline) is a direct path to a wet spark plug. This is especially true after winter or long-term storage.
• 🛢️ Poor quality fuel. Gasoline with an octane number below 92 or diluted with oil in the wrong proportion does not burn completely, leaving soot and liquid on the spark plug.
• 🔥 Spark plug wear. Insulator cracks, electrode erosion or incorrect gap (should be 0.7–1.0 mm) lead to a weak spark.
• 🌡️ Cold engine. At temperatures below +10°C, gasoline evaporates worse, and the oil in the fuel mixture thickens, impairing atomization.
• 💨 Air leak. Cracks in the pipes or a worn carburetor gasket disrupt the balance of the air-fuel mixture.
• 🔄 Air filter clogged. A dirty filter “chokes” the engine, forcing the carburetor to compensate for the lack of air with excess gasoline.

Interesting fact: trimmers with two-stroke engines (for example, Echo SRM-22GES or Makita EBH341U) the spark plug is flooded more often than with four-stroke models. This is due to the design of the lubrication system - oil in the fuel increases the risk of soot formation.

How to understand that a candle has been flooded: 3 obvious signs

Before disassembling the trimmer, make sure that the problem is a flooded spark plug. You can determine this without tools:

1. The smell of gasoline from under the starter housing or exhaust window even after several pulls of the cord.
2. No "grabbing" — the engine shows no signs of life (there are not even flashes).
3. Wet candle when unscrewing: drops of fuel are visible on the electrodes and threads, not dry carbon deposits.

⚠️ Attention: If the spark plug is dry, but covered with black soot, the problem is not in flooding, but in over-enriched mixture (needs carburetor adjustment) or ignition system malfunctions (coil, armored wire).

Step-by-step instructions: what to do if the spark plug on the trimmer is flooded

If you are sure that the problem is a wet spark plug, follow this algorithm. Do not unscrew the spark plug right away — first try to dry the combustion chamber without disassembling:

Set the choke lever to the "Choke" position.

Pull the starter 2-3 times WITHOUT pressing the gas

Open the damper halfway and try again

If it doesn’t start, unscrew the spark plug and dry it -->

If the trimmer does not start:

1. Unscrew the spark plug a special key (usually included). Pay attention to its condition:
   • 💧 Wet - filled with gasoline.
   • 🖤 Black and dry - over-enriched mixture or soot.
   • ⚪ White — lean mixture (lack of gasoline).
2. Dry the candle:
   • Wipe the electrodes with a clean, lint-free cloth.
   • Light the candle with a lighter or on a gas stove 20–30 seconds (do not overheat!).
   • Or use a hairdryer on cool air setting.
3. Check the gap between the electrodes with a probe (norm - 0.7–1.0 mm). If necessary, adjust by bending the side electrode.
4. Dry the combustion chamber:
   • Pull the starter 10–15 times without a spark plug - this will remove excess gasoline.
   • Pinch the spark plug hole with your finger and pull the starter further 2–3 times - this is how compression is created to push out the fuel.

1. Remove the air filter and check if gasoline is leaking from the carburetor.
2. Disconnect the fuel hose - if gasoline flows by gravity, the needle valve is faulty.
3. Blow out the jets with compressed air (pressure no more than 2 atm!).