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Chainsaw Dies After Cut. Tips from a Professional

Chainsaws employ a two-stroke combustion engine to deliver their sharp cutting chain power. As a result of poor maintenance, a chainsaw engine can occasionally lose power and tend to shut down despite being completely refueled. If you encounter such an issue with your machine, give this blog post a read as I guide you to solve this problem on your own without the need for any professional help.

Chainsaw dies after the cut.

If your chainsaw dies after a cut, the most common cause could be a vapor lock in the fuel tank. Open the tank’s cap for a while and see if it restarts. A plugged carburetor could also be one of the reasons and needs to be checked and thoroughly cleaned. Finally, a faulty ignition system and inadequate compression could be the factors due to which your chainsaw dies after the cut.

In this blog post, I will explain in more detail what to do. Including answering some frequently asked questions, like why a chainsaw dies at full throttle and why a chainsaw does not keep running.

Why does my Chainsaw Keep Shutting off?

If a gas chainsaw dies or won’t start, it’s always due to a fault in one of these three factors: fuel delivery, ignition system, and engine compression.

The fuel delivery system controls the fuel flow from the tank to the engine via the carburetor and fuel lines. The starting issue could be caused by any obstruction in the fuel lines that blocks the flow. In addition, the spark plug provides the ignition to begin the combustion process. A defective spark plug might cause the engine to shut down or not start at all.

Another explanation you won’t see on numerous blogs is a piston ring failure. Typically, older engines have scored cylinder walls, which contribute to increasing wear and hinder the engine from producing proper compression, resulting in the saw dying out. Let’s delve deeper into the causes of a failing chainsaw and how to repair it.

How do you Fix a Chainsaw that won’t Stay Running?

There can be multiple reasons behind dying out of a chainsaw. Let’s troubleshoot the problem by checking these causes one by one.

● 1. Fuel Vapor Lock:

A vapor lock in the fuel lines is the most typical cause of your chainsaw running slowly or dying. I’ve seen incidents when chainsaws were left out in the sun for an extended period, and when they were started, they developed this problem. The high temperature produces a vapor buildup in the fuel lines, preventing liquid fuel from entering the carburetor.

As a result of the lean combination, the saw may start perfectly. When you rev it up, the higher temperature increases the vapor pressure and entirely limits the fuel supply. When the saw is hot, this may cause it to die out.

– Solution:

To avoid this, make sure that the tank vents are not clogged with dirt or debris. These valves allow the trapped vapors to escape. Also, leave your gasoline cap open for a few minutes to allow the pressure to equalize. Then close it and restart your chainsaw.

● 2. Plugged Carburetor:

The carburetor in your machine is where air and fuel are mixed in the proper ratio. The air-fuel mixture must contain a sufficient amount of fuel to formulate a “rich” fuel mixture. Let me advise you that the contents of your fuel are very likely to develop sticky white deposits over time. These deposits can clog the carburetor jets, preventing fuel from reaching the engine. Your engine will eventually die when it is hot because it does not receive enough fuel to provide the necessary power.

– Solution:

You should get a carburetor repair kit. To clean your carburetor, first, remove the air filter. A carb cleaner spray is a great solution for dislodging the sticky deposits in your jets and getting your carb back up and running. After you’ve completed cleaning your carburetor, make sure there are no fuel residues left behind.

● 3. Defective Ignition: 

The spark plug electrode triggers combustion by producing a spark in the engine. Examine your electrode for any signs of wear and strain. Inspect the electrode for any evidence of black carbon buildup. This buildup is highly likely to occur after lengthy use and has an impact on spark quality, especially at higher firing temperatures.

– Solution:

If the electrode on your spark plug appears to be worn out, you should replace it. A good way to test your spark plug is to inject some starter fluid from the choke valve. If the engine does not start because of the fluid or if it starts and stops. Then the fault is with your ignition, and it must be corrected.

● 4. Inadequate Compression: 

Please keep in mind that the air-fuel mixture must be compressed to a suitable pressure and temperature to produce enough power in the power stroke. I recently came across a Poulan chainsaw with a single-piston ring in its engine. It was experiencing a similar problem, and upon inquiry, the fuel delivery and ignition systems were both working correctly.

However, it was later discovered that the engine’s piston ring had worn out to the point that the compression measured at high temperature was 0 psi. The piston ring typically stops gases from leaking into the crankcase during the compression stroke and maintains pressure. However, the piston’s wear rate accelerated at high cylinder temperatures due to thermal expansion, resulting in essentially little high-temperature compression.

– Solution: 

I recommend running a compression test on your chainsaw before starting it while it’s cold and after it’s been shut down due to heat. The compression tester gauge is reasonably priced and may be obtained online or at a local hardware store.

Connect the tester to the spark plug socket and pull the cable in both circumstances. Check to see whether there is a change in pressure between when the engine is hot and when it is cool. If there is a pressure difference, it implies that the problem is now in your piston and cylinder, and depending on the extent of the damage, you may require a new chainsaw.

Why does my Chainsaw Die at Full Throttle?

If your chainsaw dies at full throttle, the following can be the causes:

  • Dirty air and fuel filters
  • Blocked carburetor jets
  • Clogged muffler

When you press the throttle, the engine begins to suck more fuel from the carburetor to increase its rotational speed. If, for whatever reason, the engine does not receive an adequate amount of gasoline, it begins to draw more air, causing the mixture to become lean. As a result, the lean mixture cannot provide sufficient power to the engine at wide-open throttle (WOT). This means that there must be some obstruction, either in the carburetor or in the gasoline lines. The obstruction can be a carburetor plugged with fuel deposits or a faulty air filter gummed with debris. Eventually, this blockage causes your engine to run lean and, as a result, stall.

Why won’t my Chainsaw Keep Running?

If your chainsaw doesn’t keep running, try tuning the carburetor’s adjustment screws until it doesn’t die out. If the problem persists, investigate the fuel lines and the ignition system.

The carburetor consists of three adjustment screws, namely low-speed (L), high-speed (H), and idling screw (I). The L screw controls the amount of fuel entering the carburetor at low speed, while H controls the amount of fuel entering the carb at high speed. Idling (I) screw controls the mass flow rate of the air-fuel mixture entering the engine at idle.

Note that loosening the screw increases the fuel flow rate and enriches the mixture while tightening the screw does the opposite. If the idle screw is loose enough, the mixture would be too rich, and hence the chainsaw might not keep running even at idle. To fix this, tighten the idle screw using an appropriate screwdriver and check if the engine RPMs rise or not. Similarly, adjust the remaining screws, i.e., L and H screws, until the RPMs attain an ideal setting where the saw doesn’t die out.

Most cases of the engine shutting down could be fixed using the above adjustment method. If the problem remains unsolved, examine the fuel lines and the carburetor. Inspect the carburetor by unscrewing it and perform its cleaning if it appears necessary. Similarly, inspect the ignition system by checking the spark plug. If its quality has deteriorated, install a new spark plug in its place.

Why does my Engine Die when I give it Gas?

At a high throttle setting, a dying engine indicates that the fuel supplied to the engine is either too high or too low. This setting can be controlled by adjusting the high-speed (H) adjustment screws on the carburetor. Furthermore, a restriction in fuel delivery could also be the cause behind it.

Before adjusting the carburetor screws, it is better to troubleshoot your carburetor and air and fuel filters. It is better to clean your muffler ports as this improves compression and maximizes the engine output.

Once the initial tune-up is complete, we shall now adjust the carburetor screws to check if that was the source of the problem.

●Adjusting the Low-Speed Screw:

It is marked as L on the chainsaw. This screw controls the amount of fuel at low engine speeds. Using a screwdriver, tighten the screw to increase the fuel flow to the carburetor and eventually enrich the mixture. Keep tightening the screw until the RPMs at low speed are stabilized. Once they are stable, let’s move towards the high-speed screw.

●Adjusting the High-Speed Screw:

It is marked as H on the chainsaw. To adjust the high-speed screw, ensure your engine is turned on and the throttle is pressed wide-open (WOT). Most probably, your engine would tend to die out at WOT. To solve this, use a screwdriver to tighten the H screw on the chainsaw until the RPMs begin to stabilize. If you keep tightening it, the mixture will become too rich, and the RPMs will drop once again. Keep tightening/loosening the screw until a sweet spot is achieved where the RPMs don’t die down and remain stable at WOT.