Chainsaw Runs Good Until Hot, Tips from a Professional


Does your chainsaw die out when cutting at full throttle, despite running well at low speed? This is a common problem that mainly occurs with older chainsaw models. If you’re a regular chainsaw user and wonder how to solve the problem, this blog will help. I will list specific ways of troubleshooting the issue and fix it.

Chainsaw runs good until hot:

In general, there are four reasons why a chainsaw runs well until hot. It can be due to a vapor lock in the fuel tank. Check the fuel cap and remove any debris in the tank vents. The carburetor’s jets could be clogged with fuel deposits. The spark plug could be defective. Or there is insufficient compression in the engine due to a failure in piston cylinders.

I will look at these causes in more detail and show how to fix them. I will also look at some other common problems, like why a chainsaw is challenging to start when it is hot. Why it is getting hot and how to fix it so it will stay running.

Chainsaw Dies when Hot, what are the reasons?

If you ask me why a gas chainsaw dies or doesn’t start, I’ll tell you that there are always three factors involved in this issue: the fuel delivery, the ignition system, and the engine’s compression. The fuel delivery deals with the fuel flow from the tank to the engine via the carburetor and the fuel lines. Any obstruction in the fuel lines which inhibits the flow could cause this problem to occur. Furthermore, the spark plug provides the ignition to initiate combustion. A faulty spark plug could cause the engine to die out.

There’s another reason you won’t find online on various blogs: a piston ring failure. Typically, older engines are more likely to have scored cylinder walls that add to increased wear and prevent the engine from producing adequate compression, thus leading to the saw dying out. Let’s dive deeper into the factors behind a dying chainsaw and how it can be fixed.

1. Fuel Vapor Lock:

The most common problem causing your chainsaw to run slow or die out is a vapor lock in the fuel lines. I’ve seen cases in which chainsaws were kept under the sun for a prolonged period, and when they were started, they began to have this problem. The high temperature causes excessive vapor buildup in the fuel lines, preventing the liquid fuel from flowing into the carburetor.

This creates a lean mixture, so as a result, the saw may start perfectly. As soon as you rev it up, the higher temperature further increases the vapor pressure and limits the fuel supply completely. This may cause the saw to die out when hot.

– Solution:

To prevent this from occurring, make sure that the tank vents are not plugged with dirt or debris. These vents ensure that the trapped vapors can escape. Also, open your fuel cap for some time and allow the pressure to equalize. Then close it and start your chainsaw again.

2. Plugged Carburetor:

Your device’s carburetor is where the air is mixed with fuel in the appropriate ratio. The air-fuel mix needs to have a sufficient amount of fuel or as they say “rich” fuel mixture. Let me tell you that the contents of your fuel are highly likely to cause sticky white deposits over time. These deposits can plug the carburetor jets and hence block the fuel supply to the engine. Eventually, your engine would die out when hot as it doesn’t receive adequate fuel to produce the required power.

– Solution:

You should invest in a carburetor repair kit. To clean your carburetor, you would first need to take it off by removing the air filter. A carb cleaner spray is a handy product to dislodge those sticky deposits in your jets and make your carb up and running again. Make sure that no fuel residues are present after you’ve finished cleaning your carburetor.

3. Defective Ignition:

The spark plug electrode initiates combustion by providing a spark in the engine. Check your electrode to notice any signs of wear and tear. Check if there’s any black carbon buildup on the electrode. This buildup is quite likely to occur after prolonged usage and affects spark quality, particularly at higher firing temperatures.

– Solution:

Replace your spark plug if the electrode appears worn out. Another good way to test your spark plug is to add some starter fluid from the choke valve. Suppose the engine doesn’t start with the fluid. Or starts and stalls. The problem lies in your ignition and must be fixed.

4. Inadequate Compression:

Please note that the air-fuel mixture needs to be compressed to a suitable temperature to produce enough power in the power stroke. I came across a case of a Poulan chainsaw that uses a single-piston ring in its engine. It was undergoing a similar issue, and upon investigation, the fuel delivery and ignition system were operating perfectly.

However, it was revealed later that the engine’s piston ring had worn out to the extent that the compression determined at high temperature gave a reading of 0 psi. Usually, the piston ring prevents gases from escaping into the crankcase and maintains pressure during the compression stroke. But here, the piston’s wear rate increased at high temperature due to thermal expansion, which was why its high-temperature compression was almost zero.

– Solution:

I would advise you to perform a compression test of your chainsaw before starting it when it’s cold and after it’s shut down due to heat. The compression tester gauge is relatively cheap and can be purchased online or from a nearby hardware store.

Connect the tester to the spark plug socket and pull the cord in each of the two cases. Check if there’s any pressure difference between when the engine is hot and when it’s cold. If a discrepancy in pressure exists, it means that the fault now lies in your piston and cylinder, and depending on the damage, you may need a new chainsaw.

Why won’t my Chainsaw Start when it’s Hot?

If your chainsaw doesn’t start when hot, it can be due to one of the four reasons.

  • Air leakage into the carburetor
  • Faulty ignition module and spark plug
  • Vapor lock
  • Worn out piston rings

Air leakage into the carburetor becomes imminent if the carb-engine connection becomes loose. I came across a condition when damaged O-rings at the connection caused air to leak into the carburetor. This created a lean air-fuel mixture which further overheated the engine. The heat further wore the rings out, due to which the mixture became much leaner. Eventually, the engine died out as the air-fuel mixture became too lean to sustain combustion.

Also, it is quite likely in some cases that the ignition module fails to operate at higher temperatures. Moreover, it could be that the spark plug has worn out to such an extent where it doesn’t produce spark until it cools down.

Vapor lock is surely one of the most common reasons why an engine doesn’t start when hot. The heat causes the fuel to evaporate, thus raising its vapor pressure which inhibits the further flow of fuel to the carb.

Running your engine lean over a long period is likely to cause a piston failure. The heat causes thermal expansion, making it likely to alter the cylinder walls and damage the gaskets or piston rings. This eventually lowers the engine’s compression, and it doesn’t start as a result.

My Chainsaw Starts When Cold but Not Restart When Hot?

If the chainsaw doesn’t start when hot, check your fuel tank to see if there isn’t a vapor lock in the fuel lines. Also, check the carburetor and inspect for any leakage/fuel blockage.

Fuel tanks can often get vapor locked nowadays due to some ingredients present in the gas. Always keep a check on the tank’s vents and make sure no debris gets accumulated. Tank vents prevent vapor lock formation.

Check the carburetor’s jets and make sure that they are kept clean and free of debris. Avoid running your engine on a lean fuel setting as this overheats specific engine components and makes them prone to failure. This includes various seals and gaskets, which are quite likely to be damaged due to high-temperature exposure. This is also the key to prevent piston failure. Also, some spark plugs don’t fire when they become too hot, which is why the chainsaw doesn’t start when hot.

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

If your chainsaw won’t stay running, here are the things you can try:

  • Check if the fuel tank’s vent holes aren’t clogged with deposits. Collaged vent holes can cause vapor locks.
  • Inspect the spark plug to see if it’s workable. Inspect the ignition module with a tester.
  • Check the carburetor’s adjustment screws. A too-rich fuel setting may cause it to die out.
  • Examine the air filter and the fuel filter for debris deposits.

A rich fuel mixture is likely to stall your chainsaw. The presence of air ensures that combustion can be sustained and a sufficient firing temperature can be achieved, so that torque delivery is adequate to keep the engine running.

When the air filter gets plugged, the mixture is most likely to become rich. Hence, always inspect the filters and make sure they aren’t plugged with any debris. Ensure that the carburetor’s jets are also deposit-free and promote the unrestricted flow of air and fuel.

Also, the carburetor’s adjustment screws need to be tuned if it stalls. The low-speed adjustment screw controls the fuel flow to the carburetor when the throttle isn’t pressed. If the screw is too loose, the mixture becomes rich. Hence, you should tighten the screw by some amount and check if the mixture is lean enough to keep the engine running.

Why does my Chainsaw get Hot?

The most common reason your chainsaw gets hot are listed below:

  • Lack of lubrication between the guide bar and chain.
  • Engine running on a lean fuel mixture.
  • Chainsaw operating at wide-open throttle (WOT).
  • Inadequate oil added to the fuel mix

If the guide bar’s oil runs out, the friction due to metal-to-metal contact increases drastically. This quickly overheats the guide bar and chain. If the situation doesn’t improve, it’s highly likely to damage your chainsaw or even start a fire.

Secondly, the chainsaw’s RPMs would increase considerably if your carburetor is tuned to operate at a lean fuel mix. This also overheats the saw.  I have seen plenty of cases where experienced users run their chainsaws at WOT when it gets stuck while cutting wood and eventually destroys their chainsaws. Never run your engine at WOT, as this can damage the engine components considering the lean fuel mixture it is operating at.

Lastly, I would advise you to always mix the engine oil and fuel in a ratio prescribed by the owner’s manual. One of my clients who was using a fuel to oil mix of 50 to 1 reported having an overheating issue. It meant that there was not enough oil for the size of his engine. We changed it to 32 to 1, and most of this overheating issues were gone.

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