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Chainsaw Starts but then Dies. Tips from a Professional

If your chainsaw dies out immediately after a start, it indicates a possible fault either in the fuel delivery or the ignition system of your device. Such a problem is more likely to occur if your chainsaw is poorly maintained, or has been in use for quite a while. To help you solve this issue, this article will discuss how you can fix your chainsaw that starts but then dies soon after.

Chainsaw starts but then dies:

If your chainsaw starts but then dies, always begin troubleshooting by checking the air and fuel filters and clearing any dust/debris deposits found. Ensure that there’s no vapor lock in the fuel tank. Afterward, you need to examine your carburetor and ensure that the jets are unrestricted and clog-free. Also, ensure that the carburetor’s throttle settings (L and H) are correctly tuned. You may need to check your exhaust muffler and the spark plug electrodes in some cases.

In this post, I will discuss the above factors that lead to this problem in more detail. This will help find the best solution strategy to fix your issue. I will also show how to fix a chainsaw that won’t stay running.

Why does my Chainsaw Die when I Give it Gas?

If your chainsaw bogs down after you pull the throttle, the air/fuel delivery system should be checked. Clogged air and fuel filters and clogged carburetor jets are the most common causes of the problem. Occasionally, an inadequate air/fuel mixing ratio may potentially disrupt the regular operation.

1. Clogged Fuel Filter:

Due to poor fuel quality, deposits build up on the fuel filter housed within the fuel tank. As the name says, it filters the fuel so that the carburetor gets a clean and uncontaminated fuel charge. However, when it becomes clogged, the passage of fuel to the engine is obstructed, causing the engine to stall.

– Solution: Filter Examination and Replacement:

Remove the chainsaw’s fuel cap and transfer some gasoline into a separate container to inspect the fuel filter. The filter should then be cleaned with a dental pick or a thin metal rod. Check the filter’s quality. If the filter looks clogged, buy a new one to replace the previous filter. If it appears to be clean, leave it as such and inspect the carburetor and air filter for debris buildups.

2. Dusty Air Filter:

We can easily examine the air filter before checking the carburetor, which may be causing the chainsaw to stall. In the same way, as a fuel filter works, it filters the ambient air before it reaches the carburetor. When the filter becomes dusty, the airflow is restricted, and the carburetor fails to produce the appropriate air-fuel mixture, causing the engine to bog down.

– Solution: Air Filter Cleaning:

The air filter screen on your chainsaw is positioned on the backside. Using a screwdriver, loosen the air filter’s bolts in place. Remove the filter and look for dirt/deposits. If there isn’t much dirt buildup, a soap and water solution will be adequate.

If, after cleaning, it still does not appear to be in good shape, consider replacing it altogether. Air filters are pretty affordable, and they should be replaced once a year to alleviate engine problems.

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

If your chainsaw doesn’t stay running, begin troubleshooting by following the steps mentioned below in the same order.

1. Vapor Lock:

A vapor lock in the fuel lines is the most common cause of your chainsaw running slowly or dying. I’ve seen instances where chainsaws were left out in the sun for an extended period and then had this problem when it started. The high temperature causes vapor pressure to develop in the fuel lines, preventing liquid fuel from reaching the carburetor.

Because of the lean mix, the saw may start perfectly. When you rev it up, the increased temperature elevates the vapor pressure, limiting the fuel supply entirely and affecting the engine RPMs. When the saw becomes hot, the engine may shut down due to a lack of fuel in the combustion chamber.

– Solution

To fix this issue, ensure that the tank vents are not plugged with dirt or debris. These valves allow trapped gasoline vapors to escape. Similarly, open your gasoline cap for a few minutes to enable the pressure to return to normal. After that, close it down and start your chainsaw.

● 2. Clogged Carburetor:

Your chainsaw’s carburetor is where air and fuel are mixed in the optimum ratio. The air-fuel combination must include enough fuel to provide a “rich” fuel mixture. Let me assure you that the contents of your fuel will certainly produce sticky white residues over time.

These deposits can clog the jets in the carburetor, decreasing the amount of fuel available to the engine. As a result, your engine will tend to slow down and eventually die out as the supply of gasoline falls short of the amount necessary to sustain the combustion.

– Solution:

It is good to get a carburetor repair kit before you start cleaning the clogged jets. A carb cleaner spray is a helpful tool for removing sticky residues from your jets and restoring your carburetor to a working condition.

  • Step 1: Remove the air filter to expose the carburetor: To begin cleaning your carburetor, remove the air filter first. The air filter is usually situated right at the back of your chainsaw.
  • Step 2: Take the bowl out and clean it: Remove the bowl nut and then the bowl from the carburetor. Stale fuel and its residues are typically found in the bowl. Any residues of old fuel should be cleaned up thoroughly.
  • Step 3: Spray the carb cleaner: Clean the interior parts of your carburetor with the carb cleaning liquid. Don’t forget to wash the bowl nut, which itself is a fuel jet and is prone to blockage. When spray exits from the other end of a jet, it indicates that any debris has been removed.

● 3. Faulty Ignition:

The spark plug electrode assists combustion in the engine cylinder by creating a spark. Check your electrode for signs of wear and strain. Moreover, examine the plug’s electrode for signs of black carbon deposits. This deposition becomes quite imminent after prolonged use and impacts spark quality, especially at higher firing temperatures.

– Fixes:

If the electrode on your spark plug appears to be worn out, replace it. Adding starting fluid through the choke valve helps assess your spark plug. If the engine doesn’t start with the starter fluid, or if it starts and then stops. Then your spark plug is likely to be at fault, so it should be replaced.

● 4. Inadequate Compression:

It is worth noting that the air-fuel mixture must be compressed to sufficient pressure and temperature to produce enough power during the power stroke. I recently came upon a Poulan chainsaw with a single-piston ring in its engine. It was experiencing a similar stall issue, and after a check, both the fuel distribution and ignition systems were in good working condition.

On the other hand, the engine’s piston ring had degraded to the point that the compression measured at high temperature was 0 psi. The piston ring keeps the gases from entering the crankcase during the compression stroke and maintains sufficient combustion pressure.

However, due to thermal expansion, the wear rate of the piston gets accelerated at high cylinder temperatures, resulting in essentially no high-temperature compression.

– Solution:

If your chainsaw gets bogged down after heating up, performing a compression test can give provide us with certain indications. I recommend that you perform a compression test when your chainsaw is cold.  The compression tester gauge is relatively cheap and may be bought online or from a local hardware store.

Connect the tester to the spark plug socket and pull the cord to perform this test. Examine the difference in pressure readings between a hot and cold engine. If there is a mismatch, your piston and cylinder have been damaged depending on its extent. This would mean you may need a new chainsaw altogether.

Why does my Chainsaw Die at Full Throttle?

If your chainsaw dies at full throttle, it may be due to the following factors:

  • Dusty air and fuel filters
  • Jammed carburetor jets
  • Clogged muffler

When applying the throttle, the engine starts drawing more fuel from the carburetor to increase its RPMs. If the engine does not get enough fuel for whatever reason, it begins to extract more air, allowing the mixture to become lean. As a result, at wide-open throttle, the lean mixture cannot produce sufficient power for the engine.

This implies a blockage, either in the carburetor or in the fuel lines. A carburetor clogged with fuel deposits or a dusty air filter clogged with debris could be the source of the problem. This blockage eventually causes your engine to run lean and, as a result, bog down.

Why won’t my Chainsaw Keep Running?

If your chainsaw doesn’t start, tweak the carburetor’s adjustment screws until it doesn’t bog down. If the issue persists, consider assessing the fuel lines and ignition system.

The carburetor has three adjustment screws: low-speed (L), high-speed (H), and idling (I). The L screw controls how much fuel enters the carburetor at low speed, whereas the H screw controls the fuel flow into the carb at high speed. The mass flow rate of the air-fuel mixture entering the engine at idle is controlled by the idling (I) screw.

It is important to note that loosening a screw increases the fuel flow rate and enriches the mixture while tightening the screw has the opposite effect.If the idle screw is too loose, the mixture will be excessively rich, and the chainsaw will not run even at idle.

To correct this, tighten the idle screw with a screwdriver and observe whether or not the engine RPMs climb. Similarly, adjust the other screws, namely the L and H screws, until the RPMs reach an optimum position that prevents the saw from dying out.

The above adjustment method could be used to fix most engine problems. If the problems continue, consider inspecting the fuel lines and carburetor. Unscrew the carburetor, inspect it for damage, and clean it if necessary. Similarly, check the spark plug to assess the ignition system. Install a new one if its quality has worsened.