The situation when chainsaw stops starting after several unsuccessful attempts to start, is familiar to almost every owner of garden equipment. Most often the problem lies in one detail: spark plug becomes wet with fuel and stops producing a spark. This phenomenon is popularly known as “flooding the candle”, and it can turn the planned work of collecting firewood into a real nightmare with dancing around the instrument.
However, there is no need to panic ahead of time. Wet candle - this is not a death sentence on the engine, but only a symptom indicating an imbalance between the supply of fuel and air to the combustion chamber. Understanding the physics of the process will help you not just unscrew and wipe the part, but also eliminate the root cause so that the tool starts from the first pull of the starter in any weather.
In this article we will analyze in detail the mechanics of the malfunction, express diagnostic methods and methods of prevention. You'll find out why fuel mixture may be too rich, how to check compression and what to do if the problem lies deeper than it seems at first glance. A competent approach will save you money on the service and time on repeated launch attempts.
Mechanics of the process: why the fuel does not burn
In order for an internal combustion engine to work, a spark is required at a strictly defined point in time when the compressed air is in the cylinder. fuel-air mixture. If the spark plug is wet, this means that gasoline is entering the cylinder, but ignition does not occur. The fuel simply wets the electrodes, creating a conductive film that shorts the spark to ground or completely extinguishes the discharge.
The main reason lies in the violation of the proportions of the mixture. The two-stroke chainsaw engine requires very precise tuning carburetor. If there is little air and a lot of gasoline, the mixture becomes “rich.” It does not ignite well, especially when cold, and during repeated attempts to start with the starter, the piston simply pumps a liter of gasoline into the cylinder, unable to ignite it.
⚠️ Attention: Never try to start a “flooded” saw by continuing to pull the starter with the ignition on. This will only worsen the situation, completely eroding the oil film from the cylinder walls and potentially leading to piston scuffing.
It is also worth considering the condition of the ignition systems. Even if the mixture is perfect, a weak spark will not be able to penetrate the layer of gasoline vapor. Low voltage at the coil or a crack in the plug's ceramic insulator can be a trigger that starts a chain reaction of flooding. Therefore, diagnosis should always be comprehensive.
Diagnosis of spark plug condition
The first thing to do if there is no startup is a visual inspection. Unscrew candle with a special key and carefully examine its condition. The color of soot and the presence of moisture will say a lot about the processes occurring inside the engine. A dry but black plug indicates an over-enriched mixture, while a wet and black plug indicates that the oil is not burning completely.
Pay attention to the gap between the electrodes. It can change over time due to metal erosion or mechanical damage. A gap that is too wide requires a higher breakdown voltage, which is old ignition coil may not provide. A gap that is too narrow produces a weak spark, which is not enough to ignite a rich mixture.
- 🔍 Normal condition: Brick brown or light gray carbon deposits, electrodes are intact, the gap corresponds to the manufacturer's specifications (usually 0.6–0.7 mm).
- 💧 Filled candle: Wet electrodes, strong smell of gasoline, no spark during testing, black sticky residue.
- 🔥 Overheat: White or light gray carbon deposits, melting of the electrode, which may indicate a lean mixture or problems with cooling.
The best way to check the spark is to touch the threaded part of the spark plug to a metal part of the engine (ground) and pull the starter. The spark should be bright blue and pierce the gap with a characteristic click. If there is no spark or it is orange/yellow, the problem may not only be in the spark plug, but also in high voltage wire or ignition module.
For accurate diagnosis, always have a new, known-good spark plug of the same marking on hand. Replacing the part with a new one is the fastest way to eliminate a problem with the ignition element itself.
Carburetor and fuel system problems
The most common reason that chainsaw stalls or does not start, the carburetor is not working properly. Adjustment screws L, H and T (or LA) are responsible for fuel supply at low and high speeds, as well as idle speed. If the “L” (Low) screw is unscrewed too much, when the engine is cold, it receives excess gasoline, which it physically does not have time to burn.
In addition to settings, the state plays an important role fuel filter and system tightness. If water gets into the tank or old gasoline has lost its properties, this will also lead to starting problems. The fuel mixture for two-stroke engines has a limited shelf life, and using old fuel is a direct path to a flooded spark plug and repair.
☑️ Fuel system diagnostics
The air filter deserves special attention. If it is clogged with sawdust and dust, the engine “suffocates.” The lack of air during normal fuel supply automatically makes the mixture rich. In such conditions carburetor cannot form the mixture correctly, and the spark plug is guaranteed to flood after several jerks of the starter.
⚠️ Attention: Before adjusting the carburetor, make sure the air filter is clean and the engine is warm. Adjusting “cold” or with a dirty filter will lead to incorrect settings and unstable operation in the future.
Influence of compression and state of the CPG
Low compression is a hidden enemy that is often forgotten. To ignite the mixture, a certain pressure in the cylinder is required at the moment of sparking. If the piston group is worn out, the rings are stuck or the cylinder is lifted, the pressure drops. The fuel is not compressed to the required temperature and density, and the spark is wasted, leaving the spark plug wet.
You can check the compression using a special compression gauge, screwed in instead of a spark plug. For most household chainsaws, a normal pressure is considered to be in the range of 8–12 atmospheres. If the device shows values below 6–7 atmospheres, starting will be extremely difficult, and the spark plug will be constantly in gasoline.
| CPG condition | Compression (atm) | Probability of launch | Recommendation |
|---|---|---|---|
| New engine | 10–12 | High | Operation as usual |
| Natural wear and tear | 7–9 | Average | Monitoring, ring replacement |
| Critical wear | 4–6 | Low | Major renovation |
| Cylinder seizure | < 4 | Impossible | Replacing the cylinder and piston |
It is also worth checking the crankshaft seals. If they allow air to pass through, excess mixture enters the crankcase, disrupting the vacuum. This causes the fuel pump (membrane in the carburetor) to pump fuel unevenly, causing interruptions and intermittent flooding candles.
How to check tightness without a compression tester?
If you don't have a tool at hand, you can try to plug the muffler outlet and the carburetor inlet (if there is access), then pull the starter. If the lace bounces back with a stop, there is compression. If it fails easily, the engine “does not hold up.”
Algorithm of actions: how to dry and start the saw
If you find that candle wet, a dry start procedure must be performed. This is a standard algorithm that allows you to remove excess fuel from the combustion chamber without disassembling the engine. The main thing is to act consistently and not rush.
First, unscrew the spark plug and wipe it thoroughly with a dry cloth. Blow out the spark plug well in the cylinder to remove any gasoline that has accumulated there. To do this, you can slowly pull the starter several times with the spark plug unscrewed, after plugging the spark plug hole with a rag so as not to splash everything around.
- 🛠️ Unscrew the spark plug and remove carbon deposits (if any) with a soft brush.
- 🌬️ Blow out the cylinder and carburetor by turning the crankshaft with the starter 5-7 times.
- 🔥 Check for a spark by applying a candle to the mass.
- 🔧 Screw the candle back, observing the tightening torque.
Now the key point: move the choke lever to the “Closed” position (only if the engine is cold) and try to start it. If that doesn’t work, open the damper completely (hot start mode) and pull the starter. In this mode, more air enters the cylinder, which helps to “blow out” the remaining gasoline vapors.
The secret to a successful launch after flooding is a lot of air and a minimum of fuel. Open the choke completely and operate the starter until the first signs of seizure appear.
Prevention and seasonal storage
To prevent the problem of “constantly flooding the spark plug” from becoming chronic, it is important to follow the operating rules. Use only fresh fuel mixture, prepared no earlier than 2-3 weeks ago. Gasoline with the octane number specified in the instructions (usually AI-92 or AI-95) and high-quality two-stroke oil are the key to stable operation.
When storing a chainsaw, especially in the off-season, be sure to exhaust any remaining fuel from the carburetor. Allow the engine to stall on its own by turning off the fuel tap (if equipped) or simply waiting until the gas in the tank runs out. This will prevent the membranes from drying out and the needle sticking, which often leads to an over-rich mixture the next time you start.
⚠️ Attention: Do not store the chainsaw with a full tank of fuel for more than one month. The fuel stratifies, oxidizes and loses its properties, which is guaranteed to lead to problems with the carburetor and spark plug.
Clean regularly air filter and check the condition of the spark plug. Replacing a spark plug is a costly operation that should be carried out once a season or after a certain number of engine hours, even if the part visually seems to be in good working order. This is a cheap way to avoid difficult ignition problems.
Frequently asked questions (FAQ)
Is it possible to heat a flooded candle on a gas stove?
Technically it is possible, but it is risky. An open flame may damage the insulator or change the gap. It is better to use a hair dryer or simply replace the candle with a new one, since it is a consumable item. If you still decide to calcinate, do it carefully and only with the threaded part, avoiding direct contact of the ceramics with the fire.
Why does the candle only fill when it’s cold?
This indicates that the cold start system (choke) is not working properly or that the "L" screw on the carburetor is set too rich. During a cold start, a rich mixture is required, but if there is too much of it, it does not have time to evaporate and floods the electrodes. Try running the saw with the throttle partially open.
What spark plug gap should be on a chainsaw?
The optimal gap is usually from 0.6 to 0.7 mm. The exact value depends on the saw model and is indicated in the instructions (manual). A gap that is too small will give a weak spark, too large - the spark may not break through at low starter speeds.
Could it be the ignition coil?
Yes, if the coil (ignition module) is faulty, it may produce a weak spark or disappear when heated. It is also important to check the gap between the flywheel and the coil (usually 0.2–0.3 mm). If the gap is too large, the spark will not have enough power to ignite the mixture.