The situation when a powerful tool suddenly stops working is familiar to every owner of gardening equipment. Chainsaw won't start precisely at the moment when you urgently need to prepare firewood or saw old boards. There is no need to panic at such a moment, since in 90% of cases the problem lies in trivial things that can be easily fixed without a visit to the service center.
Before disassembling carburetor or change the piston, it is necessary to carry out primary visual and tactile diagnostics. Owners often forget basic operating rules, such as checking the fuel level or the condition of the air filter. Ignition system and the supply of the mixture requires consistent checking to eliminate false conclusions and not replace serviceable parts.
In this article we will look at the main causes of engine failure, from simple to complex mechanical failures. You will learn to recognize the symptoms and understand why. excess oil in mixture can be fatal for a two-stroke engine. A competent approach will save you money and time.
Initial check of the fuel system
The most common reason why chainsaw stalls or does not start, lies in the fuel. If the instrument has been idle for more than two weeks, the old mixture must be drained. Gasoline loses its octane properties, and oil precipitates, clogging the channels.
Check the fuel filter inside the tank. It should float freely in the liquid, and the hose should not be kinked. If the filter is contaminated with resinous deposits, the engine will not receive the required amount of fuel under load.
- 🛢️ Drain the old fuel and fill in a fresh mixture of AI-92 gasoline and high-quality two-stroke oil in a ratio of 1:40 or 1:50.
- 🧹 Rinse the fuel tank with clean gasoline if sediment or rust is visible at the bottom.
- 🔍 Inspect the fuel hose for cracks through which air may be sucked.
- 🌬️ Check the tank lid: it has a tiny hole for ventilation, its blockage creates a vacuum.
⚠️ Attention: Never use pure gasoline without adding oil to your two-stroke engine. This will cause the piston to seize and the engine to seize in a matter of seconds.
The quality of the fuel mixture directly affects the resource crank mechanism. Using low octane gasoline or the wrong oil will cause detonation. Fuel system must be absolutely sealed, otherwise adjusting the carburetor will become impossible.
Diagnostics of the ignition system and spark plugs
If the fuel is OK, the next candidate for checking is spark. Unscrew the spark plug and inspect it visually. The color of the soot will tell you more about the processes inside the cylinder than any guesswork.
A dry and black plug indicates an over-enriched mixture or poor quality oil. Wet and filled with gasoline indicates a violation of the ignition process or excess fuel during startup. Ideally, the electrode should have a light brown or grayish tint.
The spark test is carried out by placing a spark plug on the metal part of the cylinder (ground) and pulling the starter. If there is no spark, or it is very weak and red, the problem may be with the spark plug itself, the ignition coil, or the gap between the magnet and the coil.
The gap between the spark plug electrode should be 0.5–0.7 mm. If it is smaller, the spark will be weak; if it is larger, breakdown may not occur under pressure in the cylinder. Ignition module often fails after exposure to moisture or shock.
How to set the coil gap correctly?
To adjust the gap between the coil and the flywheel, use a business card or a sheet of paper 0.2 mm thick. Loosen the screws securing the coil, attach the sheet to the flywheel magnets, press the coil and tighten the screws. This will ensure optimal spark strength.
Problems with the air filter and carburetor
An internal combustion engine requires air to operate. If air filter clogged with sawdust, dust or oil, the proportion of the mixture is disrupted. The engine begins to choke, stalls at high speeds, or does not start at all.
Remove the filter cover and assess its condition. Foam filters can be carefully washed in soapy water, dried and lightly soaked in oil (if this is provided by the design). It is better to replace paper filters with new ones, since their structure is destroyed during cleaning.
The carburetor is a complex unit that requires precise tuning. Often the problem lies in a stuck needle or dirty jets. If the saw worked at the limit, and then suddenly stopped, the settings may have gone wrong quality and quantity of the mixture.
| Symptom | The probable cause is the carburetor | Elimination method |
|---|---|---|
| The saw starts and immediately stalls | Fuel nozzle or filter screen is clogged | Ultrasonic cleaning or blowing |
| The engine does not develop speed | The mixture is too lean (not enough gasoline) | Adjusting screw H (High) |
| Black smoke from muffler | Over-enriched mixture (too much gasoline) | Adjustment of screw L (Low) and H |
| Unstable idle | Air leak or dirt in channel XX | Leak testing and cleaning |
Cleaning the carburetor requires care. Use a special aerosol cleaner. It is necessary to blow out the channels with compressed air only after using chemicals. Adjustment screws L, H and T (or LA) are responsible for low, high speed and idle respectively.
Before disassembling the carburetor, take photographs of the position of the levers and springs. This will help to reassemble the unit without errors, since the design of different manufacturers (Stihl, Husqvarna, Chinese clones) may differ.
Muffler and exhaust system
It's rare, but it happens chainsaw won't start due to the banal contamination of the muffler by combustion products. Carbon deposits, when mixed with low-quality oil, turn into a dense crust that blocks the exit of exhaust gases.
Remove the muffler and inspect the outlet. If deposits are visible there, they must be burned out (if the structure is metal) or carefully removed mechanically. Do not use sharp objects that could damage the internal partitions.
After cleaning, reinstall the part. Make sure the gasket between the cylinder and muffler is intact. Burnout of the gasket will lead to air leaks and a change in the composition of the working mixture, which will again cause starting problems.
Compression and mechanical damage
If all of the above systems are working properly, but the engine is silent, the problem may be mechanical. Key parameter - compression. You can check it with a special compression tester or “by eye” by plugging the spark plug hole with your finger and pulling the starter.
If the finger does not push out, or the compression gauge shows less than 8 atmospheres, the engine requires serious repairs. Reasons for low compression: wear of the piston rings, scuffing of the cylinder, destruction of the crankshaft seals or damage to the bearings.
- 🔧 Wear of oil seals leads to air being sucked into the crankcase, which impoverishes the mixture.
- 🔩 Damage to the crankshaft bearings causes knocking and play of the connecting rod.
- 🔥 Piston seizures often occur due to running on a lean mixture or poor fuel quality.
⚠️ Attention: Operating the saw with low compression or extraneous knocking in the engine will lead to complete destruction of the crank mechanism and the need to replace the entire piston group.
Troubleshooting the engine requires disassembly. Visually inspect the connecting rod for play. Check the seals for elasticity: if they are “stiff” or have cracks, they must be replaced. Crankcase tightness - the key to stable operation of a two-stroke engine.
Starting system: starter and manual drive
Sometimes the problem is not with the engine, but with the mechanism that turns it. If the starter handle jerks jerkily or does not turn the shaft at all, you need to disassemble the starting device. Cable breakage or ratchet failure are common occurrences during active use.
Disassemble the starter housing. Check the integrity of the spring and the condition of the plastic ratchets that engage the flywheel. If they are licked, the shaft will not rotate and the saw will not be able to start.
☑️ Starter diagnostics
Lubricate the starter shaft bushing with graphite grease. This will ensure easy movement and extend the life of the unit. Trigger mechanism experiences enormous loads, so the use of high-quality materials during repairs is critically important.
If the starter is working, but the engine shaft does not rotate, the bearing may have jammed or the piston may have jammed. In this case, a complete engine repair will be required.
Frequently asked questions (FAQ)
Why does a chainsaw start and immediately stall when you press the gas?
Most often, this indicates a clogged fuel filter in the tank or an incorrect carburetor setting (the mixture is too lean at high speeds). It is also worth checking the air filter and the tightness of the intake tract.
Is it possible to start a chainsaw using pure gasoline?
Absolutely not. Two-stroke engines run on a mixture of gasoline and special oil. Starting on pure gasoline will cause instant metal-to-metal friction, overheating and jamming of the piston.
What to do if the spark plug is dry, but there is a spark?
This means that fuel is not entering the cylinder. Check if the fuel supply valve is open (if any), if the breather in the tank cap is clogged, and if the diaphragm in the carburetor is intact.
How often do you need to change the fuel filter in a chainsaw?
It is recommended to change the fuel filter once a season or every third or fourth fill-up if you use the saw intensively. A clogged filter creates a vacuum in the tank, and the saw stops starting.