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Chainsaw Stalls Out. Tips from a Professional

A chainsaw that stalls out after starting is an indicator of poor engine maintenance. Usually, this occurs when the chainsaw is kept sitting for quite a while (about a few months) or due to poor fuel quality. To help you fix this problem, I will give some possible fixes in this blog post. Hopefully, you won’t need to take your chainsaw to a mechanic after reading this.

Chainsaw stalls out:

Your chainsaw stalls out when the fuel flow to its engine gets disrupted. Usually, this happens when gasoline stored in its tank gets stale and results in the deposition of sticky white residues within the fuel lines. To solve this problem, you must ensure that the carburetor jets, the fuel lines, and the filters are clean and free from stale residues. Also, the spark plug’s electrodes need to be in working order for the engine to perform smoothly.

In this post, I will further explain why a chainsaw stalls when you give it gas and how you can fix your chainsaw if it does not want to start, along with the troubleshooting procedure.

Why does my Chainsaw Stall when I Give it Gas?

If your chainsaw stalls after giving it gas, you need to check and clean its filters. Also, the carburetor and fuel lines should be cleaned from residues of old fuel. You may also need to check your spark arrestor screen and ensure it’s unclogged.

● Reason 1: Carburetor Adjustment:

Three adjustment screws are marked on the carburetor. These are the low-speed screw (L), the idle screw (I), and the high-speed screw (H). These screws can regulate the fuel flow to the carburetor under different load conditions.

The L screw, for example, regulates the flow of fuel into the carburetor at low/idle RPMs, whereas the H screw controls the fuel flow at higher RPMs or wide-open throttle (WOT). The (I) screw is a butterfly valve that regulates idle RPMs by increasing or decreasing the air-fuel mixture’s flow.

When a screw (for example, an L screw) is tightened, the fuel flow to the carburetor is reduced, resulting in a lean mixture. This causes your engine’s RPMs to rise to a specific limit before they start decreasing. In contrast, loosening the screw loads the mixture with gasoline and reduces the RPMs to a certain level. When the L or idle screws are not correctly adjusted, the idle RPMs drop too low, causing the engine to stall and eventually shut down.

● Reason 2: Fuel Lines and Filter:

The gasoline tank, fuel filter, fuel lines, and carburetor are part of your chainsaw’s fuel delivery system. A blockage in any of these components can disrupt the fuel flow to the engine, causing it to bog down when idling. The most common cause of such jams is stale ethanol-blended fuel, which forms sticky white deposits over time.

The most common factor which results in the deposition of fuel residues is letting your chainsaw rest for an indefinite period. Ethanol blended fuels have quite a low shelf life. Hence, the quality degrades when the chainsaw is kept sitting for a while, and the narrow jets and passages get gummed up with these deposits.

As a result of this blockage, the fuel flow to the engine gets affected, and the chainsaw performance gets hindered. Sometimes, vapor locks in the fuel tank caused by insufficient venting result in engine problems. All fuel supply components must be checked one by one to overcome these issues, as explained in the following sections.

● Reason 3: Ignition and Exhaust: 

The spark plug and the ignition coil are part of the ignition system. The spark-producing quality of the spark plugs reduces over time, making it difficult to fully combust the air-fuel mixture in the combustion chamber.

Furthermore, the arrestor screen at the exhaust port that collects the spark is prone to carbon deposits. These carbon deposits can restrict the flow of exhaust gases at the exhaust stroke. Due to this, not all the combustion residues can escape the engine, and as a result of which, the engine’s compression gets reduced. This eventually takes a toll on its power and becomes prone to stall.

How Do You Repair a Chainsaw That Won’t Start?

To fix a chainsaw that won’t start, tweak the carburetor’s adjustment screws. If the problem remains, clean your carburetor and air/fuel filters. Inspect the spark plug and, if necessary, replace it.

● Step 1: Throttle Screw Adjustment:

The carburetor, as previously said, is made up of three screws (L, H, and I) that control the engine RPMs at low, high, and idle speed, respectively. If the chainsaw continues to stall, the problem may be with the low-speed and idle screws, which need to be adjusted.

– Low-Speed Screw Adjustment:

Follow these steps to conduct the low-speed screw adjustment:

  • Start the engine: Turn on your chainsaw and tighten the chain. Allow for a few seconds of idle run. Keep track of whether or not the engine idles smoothly.
  • Tighten the L screw: If the engine dies while idling, use a screwdriver to tighten the Low Speed (L) screw to raise the idle RPM. RPMs will continue to reduce as you tighten them further. Make a note of where that point is. Loosen the screw, even more, allowing the RPMs to rise until they begin to fall. Make a mental note of the location of the second point as well.
  • Find the ideal location: The perfect screw setting should now be between these two noted points. Stop turning the screw once you find the correct balance. At this point, the idle RPMs would be capable of keeping the engine running. In addition, when the trigger is pulled, the engine responds much faster and without delay.

– Idle Setting:

Because the mixture is lean enough after the low-speed adjustment to engage the clutch, the chain may begin to rotate. If your chain begins to spin, loosen the idler screw until it comes to a halt. This is critical since a rotating chain at idle is extremely dangerous for your safety. You can skip this step if your chain does not spin at idle.

The mixture composition has been optimized to keep your engine operating after the L adjustment. When the L adjustment is insufficient, you must modify your fuel delivery components, notably the carburetor and the filter.

● Step 2: Examine the Fuel System:

The carburetor must be serviced, but first, ensure that your engine’s filters are clean.

– Air Filter:

Remove the air filter cover on the back of your chainsaw with a screwdriver. Remove the filter and use a brush to clean the dust buildup. I recommended wiping it with a soapy water solution and replacing the air filter if you notice any signs of damage or wear.

– Fuel Filter:

The fuel filter is located at the bottom of the fuel tank. Before hauling it out, empty the fuel tank and keep the gasoline in an appropriate container. Remove the filter from the tank’s bottom and use a metal wire to remove the gummed-up fuel deposits from the filter. Reattach it to the gasoline tank after cleaning.

– Carburetor:

Before you start clearing the blocked jets, get a carburetor repair kit. A carb cleaner spray is a great tool for removing sticky deposits from your jets and restoring your carburetor to its original form.

  • Step 1: Detach the air filter: To begin cleaning the carburetor, remove the air filter. The air filter is usually located at the back of your chainsaw.
  • Step 2: Remove the bowl and clean it: Remove the bowl nut and bowl from the carburetor. In most cases, fuel residues and some impurities might be found in the bowl. Remove any such leftovers from the bowl thoroughly.
  • Step 3: Spray the cleaner: Spray the carb cleaner liquid into and on the carburetor’s components. Always clean the bowl nut, which is a jet susceptible to blocking. When spray exits the other end of a jet, it indicates that any debris that had become trapped has been removed.

● Step 3: Inspect the Spark Plug:

Finally, if all of the preceding techniques fail to produce results, the ignition system might have been malfunctioning. The ignition system consists primarily of a spark plug. Even if you are an amateur chainsaw operator, you should replace these spark plugs at least once a year.

The electrodes of the spark plug become damaged or accumulate carbon deposits due to frequent firing, thus lowering spark quality. In this scenario, the only option is to replace the spark plug.

● Step 4: Clean the Exhaust:

The exhaust system consists of the spark arrestor screen and the exhaust ports in your chainsaw’s muffler. To examine them, you must detach the muffler and disassemble it to access the screen and the exhaust.

Check if the exhaust ports and the screen aren’t plugged with carbon deposits. If that is the case, use a gas torch to dislodge the carbon and unclog the ports. If a torch isn’t available, use a metal wire to pluck out the deposits. Note that restricting these ports badly affects the engine’s compression and results in reduced power delivery.

● Step 5: Additional Causes:

– Vapor Lock:

Vapor lock happens when the fuel vapor pressure in the fuel tank builds up significantly and is not permitted to escape through the tank vents. As a result, the amount of fuel sucked by the carburetor decreases, leading the engine to shut down. 

To confirm if there’s a vapor lock, remove the tank’s cap and place it back on again. The engine should be running by now. Always keep your tank vents clean and unclogged as a precaution.

– Air Leakage:

This may be one of the least common causes of the condition, but it does occur in some cases. The engine and its accompanying delivery system must be airtight to maintain proper temperature and pressure. Certain engine components, such as the crank seals and head gaskets, wear out and leak after extended use.

Air leakage has the effect of changing the composition of the air-fuel mixture. As a result, the engine runs at too high or too low RPMs. A pressure test on your chainsaw will help you determine if there is air leakage. Once the damaged seal or gasket has been found, it must be changed, and the engine should be operational again.