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Chainsaw Dies after Letting off the Throttle. Tips from a Professional

Have you ever wondered why your gasoline chainsaw starts running low just after letting off the throttle? The fault most certainly lies in your engine and its fuel delivery system. To help you solve this problem by yourself, this blog post shall discuss various causes that keep your chainsaw from running seamlessly. It shall also focus on the possible strategies that can be implemented to resolve the issue.

Chainsaw dies after letting off the throttle. Tips from a professional

If your chainsaw stalls after the throttle’s released, ensure that your air and fuel filters are clean and deposit-free. Examine your carburetor jets for fuel residues that could restrict the fuel flow and result in engine stalling or not starting at all. In some cases, a vapor lock in the fuel tank and a faulty ignition system can also trigger such problems.

In this blog, I will further give more insight on various causes that facilitate engine problems and what would cause a chainsaw not to idle.

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

If your chainsaw engine doesn’t keep running after releasing the throttle, begin your troubleshooting by investigating the factors described in this section. These steps are mentioned in increasing order of complexity. If the initial easier steps don’t yield success, move next towards more advanced steps till the issue is resolved.

● 1. Vapor Lock:

The most common cause of your chainsaw operating slowly or dying out is a vapor lock in the fuel lines. I’ve seen cases where chainsaws were left out in the sun for a longer duration and then had this problem when they were started. Because of the high temperature, vapor accumulates in the fuel lines, preventing liquid fuel from approaching the carburetor.

The saw may start perfectly as a result of the lean mixture. When you rev it up, the higher temperature raises the vapor pressure, limiting the fuel supply altogether. When the saw gets hot, the engine may die out due to insufficient fuel being fed to the combustion chamber.

– Solution

To prevent this, ensure the tank vents are not blocked with dirt or debris. The trapped gasoline fumes can escape through these valves. Likewise, open your gasoline cap for a few minutes to allow the pressure to normalize. Afterward, close it and start your chainsaw.

● 2. Clogged Carburetor:

Your chainsaw’s carburetor is where the air and fuel are mixed in the appropriate ratio. The air-fuel mix must include enough fuel to provide a “rich” fuel mixture. Let me tell you that the contents of your fuel will most certainly develop sticky white deposits over time. These deposits can choke the jets in the carburetor, limiting the fuel to the engine. When your engine is overheated, it will eventually die down because it does not receive enough gasoline to deliver the requisite power.

– Solution:

Get yourself a carburetor repair kit before you begin cleaning the clogged jets. A carb cleaner spray is an excellent tool for dislodging the gummy deposits in your jets and restoring your carburetor to a working state.

  • Step 1: Access the carburetor: To begin cleaning your carburetor, remove the air filter to uncover your carburetor. The air filter is typically located towards the rear side of your chainsaw.
  • Step 2: Remove and clean the bowl: Remove the bowl nut from the carburetor and remove the bowl. The bowl usually includes expired fuel and its subsequent residues. Any residues and old gasoline should be removed.
  • Step 3: Spray the interior with carb cleaner: Spray carburetor cleaner liquid over the inside sections of the carburetor. Don’t forget to clean the bowl nut, which is itself a jet that is more vulnerable to clogging. When the spray comes out of the other end of a jet, it implies that any debris has been cleared.

● 3. Faulty Ignition:

The spark plug electrode facilitates combustion in the engine cylinder by providing a spark. Look for signs of wear and strain on your electrode. Also, examine the electrode for signs of black carbon deposition. This accumulation is quite likely to occur after prolonged usage and affects spark quality, particularly at higher firing temperatures.

– Solution:

Replace the electrode on your spark plug if it appears to be worn out. Injecting starting fluid from the choke valve is a good technique to test your spark plug. If the engine won’t start due to the fluid, or if it starts and stops. Then the issue lies with your ignition, which needs to be replaced.

● 4. Poor Compression:

It is important to remember that the air-fuel mixture must be compressed to sufficient pressure and temperature to generate enough power in the power stroke. I recently discovered a Poulan chainsaw with only one piston ring in its engine. It had a similar stall problem, and after inspection, the fuel distribution and ignition systems were operational.

The engine’s piston ring, however, had deteriorated to the point that the compression measured at high temperature was 0 psi. The piston ring normally prevents gases from seeping into the crankcase and maintains pressure during the compression stroke. However, because of thermal expansion, the piston’s wear rate increased at high cylinder temperatures, resulting in almost zero high-temperature compression.

– Solution:

I recommend performing a compression test before starting your chainsaw while it’s cold and after it’s been stopped down due to heat. The compression tester gauge is quite inexpensive and may be purchased online or at a local hardware shop.

While performing this test, connect the tester to the spark plug socket and pull the cable. Check the difference in pressure between when the engine is hot and when it is cool. If there is a pressure mismatch, it means that the fault lies in your piston and cylinder, and depending on the amount of the damage, you may need to replace your chainsaw altogether.

Why does my Chainsaw Bog down when I Pull the Trigger?

If your chainsaw bogs down after pulling the throttle, the air/fuel delivery system needs to be examined. In most cases, clogged air and fuel filters and blocked carburetor jets are causing the problem. In some cases, an incorrect mixing ratio of the air/fuel mixture could also end up disrupting the normal operation.

●1. Clogged Fuel Filter:

Deposits accumulate on the fuel filter located within the fuel tank as a result of low fuel quality. As the name implies, it filters the fuel so that the carburetor receives a clean and uncontaminated gasoline charge. However, when it becomes blocked, the flow of fuel to the engine is disrupted, causing the engine to stall.

– Repair: Fuel Filter Inspection and Replacement:

To inspect the fuel filter, remove the chainsaw’s fuel cap and pour some gasoline into a different container. Then, using a dental pick or a thin metal rod, filter the tank. Examine the filter’s quality. If it appears to be clogged, purchase a new filter and replace the old one. If it appears clean, leave it be and examine the carburetor and the air filter for buildups.

●2. Dusty Air Filter:

Before we check the carburetor, we can easily inspect the air filter, which could be causing the chainsaw to stall. It filters the ambient air before it reaches the carburetor in the same way as a fuel filter does. When it becomes dusty, the airflow gets affected, and the carburetor fails to produce the necessary air-fuel mixture, causing the engine to bog down.

– Solution: Cleaning the Air Filter:

Your chainsaw’s air filter screen is located on the rear side. Loosen the fasteners that hold the air filter in place with a screwdriver. Remove the filter and inspect it for dirt/deposits. A soap and water solution will be sufficent if the dirt buildup isn’t much.

However, if it still does not appear to be in good condition after cleaning, consider replacing it entirely. Air filters are rather inexpensive, and you should replace them once a year to minimize engine problems.

Note: If your engine still faces difficulty after cleaning the filters, consider examining your carburetor for any fuel deposits using the steps mentioned above.

Why does my Chainsaw Run only on Choke?

When a chainsaw runs only on a choke, the problem certainly lies in the fuel delivery system consisting of the fuel filter, fuel lines, and the carburetor.

The choke switch helps start an engine by increasing the quantity of fuel reaching the engine, or ‘enriching’ the air-fuel mixture in other words. After the engine starts, the choke is usually turned off. However, when some chainsaw engines are deprived of fuel and run leaner than normal, then they can only run when the choke is kept on.

Possible causes of this problem are:

  • Improperly mixed oil and fuel: For two-stroke engines, fuel and engine oil are mixed in a ratio of 50:1. When chainsaws become old, most users like running them lean and use lower mixing ratios such as 30:1 or 25:1. This could induce starting difficulties in some chainsaws that have faulty filters and old carburetors, and hence they can only be kept running when the choke is on.
  • Defective fuel filter: As explained above, a blocked fuel filter starves the engine from an adequate amount of fuel, and hence the engine runs leaner than normal, causing it to run only when the choke is on.
  • Carburetor issues: When carburetors aren’t serviced regularly, they too can make the air-fuel mix lean by restricting the fuel jets, and the engine faces trouble starting.

What Would Cause a Chainsaw to not Idle?

If a chainsaw doesn’t idle, check the carburetor’s idle and low-speed screw (L) setting. Adjusting the screw setting solves the problem in most cases. In other cases, tuning of carburetors and filters may be needed along with screw adjustment.

The low-speed screw (L) controls the amount of fuel when the engine is at idle speed. Tightening the screw inhibits fuel flow and makes the mixture lean, while loosening it enriches the mixture with fuel. To adjust the screw, start your chainsaw and let it idle for a few seconds. If it dies down, tighten the L screw with a screwdriver till the RPMs begin to increase. Keep tightening the screw until the RPMs begin to drop after a certain limit. Make a mental note about this point’s location.

Next, begin loosening the screw until the RPMs increase and keep loosening till the limit is reached, after which they start decreasing again. Make a note about this second point’s location. Keep adjusting the screw between these two points until a sweet spot is reached where the engine runs at optimum RPMs and doesn’t die out when idling.

Apart from L screw adjustment, a fine-tuning of the chainsaw engine involving servicing of its carburetor and fuel delivery components further improves the idle response and makes the engine run smoother.