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Chainsaw Vapor Lock. Tips from a Professional

Chainsaw engines are prone to get overheated during use. Not only does overheating affect the components’ life, but it also contributes to a vapor lock, which makes it challenging to start the engine. Quite often, the users are unaware of a chainsaw vapor lock and the possible risks associated with it; hence I shall discuss this issue in detail in this blog post.

Chainsaw vapor lock:

A chainsaw that is vapor-locked has trouble starting just after a run. The gasoline vapors accumulated in the fuel lines exert backpressure, depriving the engine of sufficient fuel. In most cases, opening the fuel tank’s cap allows the vapors to escape into the environment. To prevent this condition, always make sure you run your engine idle for a few minutes before shutdown and never operate it at WOT.

I will further explain why a vapor lock develops, how you can fix it, and how you can stop a chainsaw vapor lock. At the end of the article, I will also show why your chainsaw can die when it is hot.

How do I Know if a Chainsaw Engine has a Vapor Lock?

If your chainsaw engine has a vapor lock, it will start perfectly, but as it heats up, it would act as if it’s run out of fuel. In some cases, it wouldn’t start up just after you’ve turned the engine off.

Vapor lock is a condition when gasoline vaporizes excessively in the fuel tank and the fuel lines. As a chainsaw heats up, the vapor pressure in the fuel lines increases. This heating effect worsens when the saw is run at wide-open throttle (WOT) or when the carburetor is adjusted to a lean setting.

As the vapor pressure builds up, the carburetor faces difficulty extracting gasoline through the fuel lines due to the backpressure created by the vapors. The engine, as a result, starves from fuel, and hence it may not start again after it has been shut down after a heated operation.

Usually, all fuel tanks have vents to allow the escape of fuel vapors into the atmosphere. Hence the vapor pressure doesn’t escalate too much to trigger a vapor lock. If you experience that your overheated chainsaw doesn’t start up, check your tank vents for any clogging.

Also, in the case of vapor lock, the chainsaw starts just fine when it is cold and runs perfectly too. As it begins to heat up, it might show signs of bogging down and feel like the fuel has run out. If, in this case, you shut the engine off and restart it without checking the fuel tank, it would not start again. This would confirm that your engine has indeed developed a vapor lock.

How do you Fix a Chainsaw Vapor Lock?

One way to fix a vapor lock is to open the fuel tank’s cover and allow the vapors to escape the fuel lines. However, the safest way of fixing this is to allow your chainsaw to cool for some time before starting it again.

Fastest Way:

As discussed earlier, fuel vapors are trapped in the carburetor and fuel lines. These vapors exert an additional back pressure, thus hindering the fuel flow to the engine. The quickest way of removing these vapors is to allow them to escape back into the atmosphere. This can be done by opening your fuel tank’s cover and letting all the vapors escape.

As the vapor pressure falls, the fuel flow will ease down, and the engine will start as a result. This method, however, is certainly not the safest. It can be risky to let highly pressurized fuel vapors escape into the atmosphere as they tend to ignite and start a fire, particularly in a closed environment. Furthermore, if these vapors are hot enough, they may cause burns to your skin.

Safest Way:

The safest way is to ensure these vapors cool down and condense within the fuel lines. To do this, you can stop your engine and let it sit for a while. This may be more time-consuming if you want to start quickly. To speed up the process, you can pour some cold water on the carburetor and the engine area. This will further help cool down the vapors and fix the vapor lock.

Useful Tip:

Some users turn the choke on and set their carburetor to a rich setting when they encounter a vapor lock. They do so to enrich the mixture with more fuel, which was restricted due to the vapor lock. I wouldn’t recommend this, as after the vapor lock is fixed, your engine would run a lot richer and may experience difficulty while running.

This can also unnecessarily increase your device’s fuel consumption. Also, avoid adjusting your carburetor to a lean setting, which causes overheating and further aggravates the vapor locking effect.

How do you Stop a Chainsaw Vapor Lock?

To prevent your chainsaw from vapor locking, avoid running it lean or overheating it. Ensure you always let the engine idle before shutting it off.

Vapor locks can be quite frustrating if you have work to finish. To save yourself from the trouble of fixing them over and over, here are some tips and tricks that can help you prevent chainsaw vapor locks.

1. Avoid Running at WOT:

Running your chainsaw at wide-open throttle (WOT) overheats it excessively. I would never recommend you to run your saw at WOT for more than a short period. The heat generated is enough to boil the gasoline, thus causing a vapor lock. Prolonged operation at WOT can even cause damage to the engine components along with the guide bar and chain.

2. Avoid Running Lean:

Most users like running their newer chainsaws lean as this saves them fuel and provides them with higher RPMs to cut through tougher wood. The L and H screws at the carburetor make the mix either rich or lean, depending on their adjustment. It would be best to understand that lean mixing ratios can cause your chainsaws to overheat and eventually result in a vapor lock.

3. Idle Before Shutdown:

Vapor lock often occurs when you restart a chainsaw that has just been hot after an operation. Before shutting your engine, I recommend letting it idle for a minute or two. Doing this would cause a gradual drop in the engine temperature, and the fuel vapors would also cool down. Hence, when you restart the chainsaw, it won’t get vapor locked.

4. Keep a Check on the Fuel:

Most chainsaw-related issues arise during the transition from winters to summers. Fuel blend during winters is often lighter than that used in summers; hence, it vaporizes at a comparatively lower temperature. This is often the case when the temperature rises at the onset of spring. Therefore, you should check the fuel and ensure that a summer-blend fuel is used during summers to avoid vapor lock issues.

5. Store it in a Cool Place:

As you sometimes see, never place your chainsaw out in the sun, as this is the easiest way of getting a vapor lock. Even after you’ve paused your work, please place it in the shade away from the sun so it doesn’t get hot. A chainsaw kept in the sun will have a higher chance of developing issues when starting up due to a buildup of fuel vapor pressure in the lines.

6. Keep the Vents Clean:

Perhaps the most important and yet the most ignored trick is to keep the vents of your fuel tank clean and deposit free. These vents are especially created to prevent any vapor buildup in the fuel tank and are likely to get plugged with dust and debris. Use a thin metal wire to keep them fully opened and clean.

Why does my Chainsaw Die When Hot?

If your chainsaw dies when hot, it may be due to a clogged arrestor screen or filters plugged with debris. A restricted carburetor or a vapor lock in the fuel lines could also be the reason behind a chainsaw dying when hot.

There can be multiple causes behind a chainsaw that bogs down when overheated. Some of the major causes are:

1. Clogged Spark Arrestor:

The spark arrestor screen is a meshed wire that catches and diminishes spark at the exhaust port. Due to rich settings, the arrestor screen gets plugged with ash and soot deposits. Hence, the engine’s compression gets lowered, which may not be enough to keep the chainsaw running.

To fix this problem, the exhaust muffler needs to be disassembled, and the arrestor screen should be cleaned thoroughly with a torch flame till the plugged deposits have been dislodged completely.

2. Blocked Filters:

Whenever you experience that your engine is delivering lesser power than usual, always begin by checking the filters first. The air filter is located underneath its cover at the rear end of the saw, while the fuel filter can be found in the tank bottom at the start of the fuel line that leads to the carburetor. Both these filters should be cleaned and must be free from any debris.

To clean the air filter, use a wire brush and a soap water solution so that no dust or debris remains. For the fuel filter, insert a thin metal wire into the filter to dislodge any stale fuel remains.

3. Faulty Carburetor:

The carburetor is the main agent where the air and the fuel meet before entering the engine. Usually, 90% of the problems are likely to occur at the carburetor. The carburetor jets need to be kept entirely clean from fuel deposits. Furthermore, you must ensure that its internal components, such as the diaphragm, aren’t worn out.

Apart from that, the carburetor’s adjustment screws need to be properly adjusted so that the chainsaw is tuned to an optimal fuel setting. This would prevent bogging down at high RPMs.

4. Vapor Lock:

If a chainsaw is overheated due to a lean run or higher ambient temperature, it’s prone to getting vapor locked. To fix a vapor lock, keep your tank’s cap open for a while to allow the gasoline vapors to escape from the fuel lines. Alternatively, you can cool down your chainsaw by pouring cold water over the fuel tank while keeping the engine off.