The situation when a chainsaw Stihl MS 180 The spark plug floods and stops starting is a classic problem for owners of this popular tool. Most often this happens after a series of unsuccessful starting attempts, when the user, without receiving a spark in the cylinder, continues to pull the starter, pumping more and more fuel into the combustion chamber. As a result, the spark cannot penetrate the wet gap, and the engine stalls or completely refuses to respond to manipulation.
The root of evil lies in the imbalance of the fuel mixture entering the cylinder. Over-rich mixture displaces the air necessary for combustion, making ignition impossible. To bring the saw back to life, it is necessary not only to replace the spark plug, but to understand why the fuel supply system failed and eliminate the root cause, otherwise history will repeat itself after a few hours of operation.
Mechanism of soot formation and symptoms of overflow
When chainsaw Shtil 180 stalls and does not start, the first indicator of the problem is the appearance of the spark plug. If you unscrew it and see a wet, black residue with a strong smell of unburned gasoline, this is a direct sign that too much fuel is entering the cylinder. A dry spark plug, on the contrary, may indicate problems with the supply or spark, but in our case we are considering the “flood” scenario.
The filling process occurs in stages. First, the carburetor supplies an excess amount of emulsion, then the fuel does not have time to burn and settles on the electrodes. Spark discharge loses power, since gasoline is a dielectric in a liquid state. The engine begins to “sneeze”, shoot into the muffler and eventually completely stops responding to the jerking of the starter.
If the spark plug is wet, but there is a spark and it is powerful (blue), the problem lies precisely in the quality of the fuel mixture or compression, and not in the ignition system.
It is important to distinguish between a simply wet spark plug after a long period of inactivity and a spark plug that was flooded when trying to start. In the first case, it is enough to dry the parts, in the second, intervention in the settings is required carburetor or checking the tightness of the system.
⚠️ Attention: Never try to start the saw with the spark plug unscrewed if gasoline is splashing in the cylinder - this can lead to water hammer and serious damage to the piston group.
Diagnostics of the condition of the spark plug and ignition system
The first step in troubleshooting should be a thorough visual inspection. Unscrew the spark plug and inspect it carefully. The color of the insulator and the condition of the electrodes will tell about the processes occurring inside the engine. The normal color is light brown or brick. Black, shaggy soot indicates a rich mixture, while white means a lean mixture or overheating.
Checking for sparking is a critical step. Place the spark plug threads against the metal of the engine (cylinder) and pull the starter. The spark should be bright, blue and audible. If the spark is red or barely noticeable, the problem may not be with the fuel, but with the ignition coil or the spark plug itself. However, if the spark plug is wet, there may be no spark at all due to a short circuit to ground through the fuel layer.
If visual inspection confirms that Stihl MS 180 really flooded, you need to dry the cylinder. To do this, remove the spark plug, turn the saw over with the spark plug hole facing down, and vigorously pull the starter several times. This will help expel excess fuel from the combustion chamber. After this, wipe the candle with a dry rag, heat it over a flame (if possible) or simply let it air dry.
Carburetor adjustment: eliminating overflow
The main reason why I drank Calm 180 If the spark plug is flooded, the carburetor adjustment is incorrect. In particular, the screw is responsible for the amount of fuel at idle and during startup L (Low). If it is turned too far, the mixture becomes excessively rich, which leads to starting problems.
For correct adjustment you will need a screwdriver. Locate the adjustment screws on the carburetor body. Standard factory setting for propeller L Usually it is about 1-1.5 turns from the fully tightened state, but the exact value depends on engine wear and operating conditions. Adjusting screw L should be done on a warm engine, but if the saw does not start, you can try to set the basic values “by ear” and by reaction.
☑️ Basic setup of a Stihl carburetor
If after tightening the screw L clockwise (the mixture becomes leaner), the saw starts up easier, which means that the problem was precisely over-richness. However, if the adjustment does not help, the seal may be broken or the jets may be dirty.
| Screw | Function | Clockwise rotation | Counterclockwise rotation |
|---|---|---|---|
L (Low) |
Low RPM/Startup | Leaning the mixture | Mixture enrichment |
H (High) |
High RPM/Power | Leaning the mixture | Mixture enrichment |
LA (T) |
Idling | Increase in speed | Reducing speed |
⚠️ Attention: Screw H (High) on new saws is often closed with a plastic stop. Do not try to remove it and turn it without a tachometer - this may cause the engine to operate at excessive speeds and cause it to jam.
Checking the fuel system and filters
A clogged fuel filter or air filter can dramatically change the mixture. If the air filter chainsaws contaminated with sawdust and dust, less air enters the carburetor and the mixture automatically becomes richer. This is one of the most common reasons why a tool stalls under load or has difficulty starting.
Remove the air filter cover and assess the condition of the filter element. If it is black and clogged, it must be replaced or thoroughly washed (if the material allows it). Also check the fuel filter inside the tank. If it is clogged, gasoline may flow in jerks, creating the effect of either a lean or rich mixture, which throws off the carburetor settings.
Pay special attention to the fuel line. The tubes become tanned over time and may crack, allowing excess air to pass through. Air leak after the carburetor leads to a lean mixture, but air leaks before the carburetor (in the gas tank) or leaks in the crankshaft seals can disrupt the operation of the entire system. Check the integrity of the hoses and their tightness to the fittings.
How to check the tightness of the seals?
To accurately diagnose air leaks through the crankshaft seals, a special device is required - a pressure tester. At home, you can spray WD-40 on the seals while the saw is running: if the speed changes, it means the seal is broken.
The influence of fuel and oil quality on starting
The quality of the fuel used plays a decisive role in the stability of the two-stroke engine. Stihl MS 180 requires the use of gasoline with an octane rating of at least AI-92. Using low-quality fuel or gasoline that has expired (more than 2-3 weeks after mixing with oil) leads to separation of the mixture and the formation of resins.
Resins settle on the walls of the carburetor, stick in the jets and disrupt the patency of the channels. This can lead to the carburetor needle not tightly shutting off the fuel supply, and the chamber will overfill even when the engine is not running. Old fuel loses its properties and burns worse, requiring a more powerful spark, which a wet candle cannot provide.
It is also important to maintain the correct mixing ratio of oil and gasoline. For Stihl saws, the recommended ratio is 1:50 (20 ml of oil per 1 liter of gasoline) when using original oil Stihl HP Ultra. Excess oil in the mixture also contributes to the formation of soot and spark plug flooding.
Use only fresh fuel mixture, prepared no more than 2-3 weeks ago, and store it in a special fuel canister, not in a plastic water bottle.
Algorithm of actions when a candle is flooded
If your chainsaw Shtil stopped starting and you suspect a flood, proceed according to the following algorithm. First, remove the air filter and make sure it is clean. Then remove the spark plug. If it is wet, wipe it dry and blow out the cylinder as described above.
Next, check for spark. If there is no spark, replace the spark plug with a known good one. If there is a spark, but the plug is wet again after a couple of attempts, then the problem is carburetion. Try starting the engine with the choke fully open (hot start mode) by pressing the throttle trigger. This will purge excess air into the cylinder.
In cases where simple methods do not help, a deeper cleaning of the carburetor will be required. Remove it, disassemble it, blow all channels with compressed air and wash with a special cleaner. Often the problem is solved by replacing the carburetor membrane or needle, which lose elasticity over time.
How to properly dry a flooded candle?
The best way is to wipe with a rag and heat over the fire of a gas burner or lighter for 10-15 seconds. Do not keep the candle in the flame for too long to avoid damaging the insulator. After calcination, let it cool naturally without cooling with water.
Can I use a spark plug from a car?
No, absolutely not. Spark plugs for two-stroke engines have a different glow number and design. Installing a car spark plug will lead to failure of the piston group or the spark plug itself due to improper thermal conditions.
Why does the saw start and immediately stall?
This could be a sign of a clogged fuel valve in the tank cap (creating a vacuum), a clogged muffler, or an incorrect idle screw setting. LA. It is also worth checking whether air is being sucked through the gasket under the carburetor.
What gap should be on a Stihl MS 180 spark plug?
The optimal gap between the electrodes is 0.5 mm. It is best to check and adjust it using a feeler gauge. Too large a gap will require more voltage to break down, which can be critical for an old ignition coil.