Chainsaw Starts And Stalls. Cause.

The owners of chainsaws sometimes have to deal with the fact that the saw, for no apparent reason, stops working normally. To find out why the chainsaw stalls under different operating modes, and also describe how to diagnose a malfunction, we will try in our article.

Why chainsaw stalls when heated?

The situation in which the chainsaw on the cold starts, and in the process of heating may stall, is familiar to many who have to deal with them. The main reasons for this behaviour are as follows.
Faulty ignition module (coil). You can determine the fault by checking the spark first on a cold engine, and then on a hot one. If there is no spark on a hot engine, then it is worth trying to eliminate the problem by replacing the ignition coil.

You can check the ignition coil with a multimeter or by replacing it with a known good one. The multimeter test of the primary and secondary windings is carried out in the resistance measurement mode. The resistance indicator of the primary winding, the working coil, is one kΩ. secondary 4 kΩ.

Why chainsaw stalls under load?

In some cases, the chainsaw under load is unable to work normally and just stalls. A common reason for this behaviour is improper carburetor adjustment or air leakage through crankshaft oil seals or a carburetor gasket. And also this behaviour can occur due to the leakage of the carburetor.

To diagnose the cause and eliminate the fact that the chainsaw starts and stalls under load is best in the service center, because special tools are needed to check the tightness of the carburetor and engine crankcase.

A saw unable to work under load will also uncertainly maintain idle speed. They will “swim.” Diagnostics begin with a tightness test crankcase and carburetor. If air leakage through crankshaft oil seals is detected, they must be replaced. Upon detection of air leaks in the carburetor, you can eliminate the cause by installing a repair kit.

Only after the above actions have failed and the engine crankcase with the carburetor is sealed, you can begin to adjust the carburetor.

The reason for this algorithm is as follows, if the air suction from the crankcase is not eliminated, but the carburetor was simply adjusted to normal engine operation, the fuel mixture will contain more fuel than it is required with a sealed crankcase, which in turn will significantly increase its consumption. Also, most likely, carbon will appear in the engine, which will also adversely affect the future work of the chainsaw.

In some models of chainsaws, to ensure the operation of the fuel pump, special hoses are installed, which transmit an air pulse from the engine crankcase to the carburetor fuel pump. If this hose breaks, the saw will run unevenly at idle and will not work at all under load.

Owners of household chainsaws HUSQVARNA 137 and HUSQVARNA 142 with any deviations from the engine from the norm, you must first check the pulse hose, because it is considered the most common cause of failure of these chainsaws.

Why the chainsaw is not gaining momentum and stalls?

If the chainsaw is not able to gain momentum a minute after start-up or stalls when you press the gas trigger, most likely the carburetor or crankcase of the engine are leaking. As in the previous case, the problem can be solved by checking for tightness and adjusting the carburetor.

If the chainsaw does not gain momentum and stalls after it has worked normally for about 5 minutes, the reason may be a defective fuel tank vent. The vacuum created in the fuel tank during the operation of the tool does not allow the engine to receive the necessary amount of fuel for its normal operation, and for this reason, it will be unable to gain momentum or stall. At the same time, if you stop the tool, open and close the fuel tank lid and start the chainsaw again, the tool will normally work again for about five minutes, after which it will stop picking up speed or stall.

The reason that the chainsaw is not gaining momentum may be excessive soot in the muffler, which makes it difficult to release exhaust gases, thereby reducing engine power and speed.

If desired, the need to check the tightness of the crankcase, but the lack of a special tool, you can use the following test method.

Crankcase leak test algorithm:

  • Remove the side cover and tire from the chainsaw.
  • Unscrew the spark plug and put a string with knots into the cylinder through the plug hole, thereby stopping the movement of the piston and crankshaft.
  • As a lace with knots, you can use the old cord from the starter, imposing on it knots in 3-5 cm.
  • Unleash the leading sprocket chainsaw.
  • Remove the oil pump cover and the pump itself.
  • Remove the starter from the chainsaw.
  • Unscrew and remove the flywheel.
  • Remove the carburetor.
  • Using a syringe, through the hole under the carburetor in the cylinder, pour gasoline into the crankcase, while watching the crankshaft oil seals. If gasoline will flow through them, then the glands have become unusable and must be replaced with new ones.
  • Installation of glands is better to entrust professionals.

An indirect sign of crankcase leakage are oil leaks in the area of ​​the glands.

Why does the chainsaw start and immediately stalls?

The chainsaw starts and stalls immediately, the reason for this behaviour may be hiding in the carburetor. Malfunction of the fuel pump or malfunction of the main fuel jet can cause this behaviour of the saw. The inability of the chainsaw to work after the launch requires a full diagnosis in the service center.

All of the above options for the engine malfunction have similar reasons, which, depending on their neglect, can have different manifestations. For example, with a slight leakage of air into the engine crankcase, its operation will not change much, the engine’s capacity will drop slightly, its maximum speed will increase, and it will be able to heat up a little more. At middle stages of air leaks, the engine will stop working at idle and will be very hot during operation. Strong air leaks will make it impossible for the saw to work, it will start up and immediately stall.

In parallel with the visible manifestations of malfunctions, for example, inoperability of the chainsaw after starting, inside the engine at the time of its malfunction, there will undergo processes that irreversibly lead the saw to the most serious consequences, for example, melting the piston, jamming the crankshaft.

Malfunctions leading to malfunction of the chainsaw.

There are a number of faults that must be considered when diagnosing, because they can lead to interruptions in the work of the saw.

  1. Worn crankshaft bearings. When worn crankshaft bearings, inevitably the appearance of a beating on the main shaft, where the flywheel is attached. In such a situation, it is impossible to adjust the gap between the flywheel and the ignition coil, which leads to interruptions in the sparking and unstable operation of the chainsaw.
  2. Contamination of the pulse channel. The impulse channel serves to ensure the operation of the fuel pump. Respectively, its pollution leads to incorrect operation of the pump, which will make it impossible for the saw to work (it will start and immediately stall).
  3. Wear CPG. As a rule, with increased wear of the CPG, there is a decrease in compression in the engine of the chainsaw, which will necessarily affect its ability to develop revolutions.
  4. Contamination of the fuel and air filters.

Summing up.

When the first signs of a malfunction of the chainsaw, it is necessary to conduct a full diagnosis. To avoid damage to the saw as a result of improper maintenance, it is better to entrust the work of determining and repairing engine malfunctions to professionals. And most importantly, do not need to use a chainsaw with minor defects, because this will lead to even greater problems.