Chainsaw Won’t Stay Running? Check Out Our Guide!

It’s annoying when you are ready to start a job and one of your tools fails. It’s even worse when the tool seems to be working fine and it suddenly stops. Try to relax and read our guide to possibly find the reason why your chainsaw won’t stay running.

There are many factors that can stop your chainsaw from running, including a bad spark plug or dirty air filter. There are simple problems: a broken fuel line, bad fuel, wrongly calibrated high-low adjustment screw. Also, more complex issues like a damaged carburettor or an engine compression problem.

Below you will find a list of the most common problems that keep a chainsaw from staying running. Also, some ideas about how to fix them, and when it’s time to consider asking for professional help.

Simple reasons why your chainsaw won’t stay running

The very first step you should take is to check your chainsaw manual. Make sure you understand the basic ins and outs of your chainsaw to make it easier to identify the problem. Then you can try matching up the problem with one of our explanations below.

Old Gas / Bad Fuel – When was the last time you refuelled your chainsaw?

Something that most people don’t think of is that the volatile components of gas evaporate when it has been sitting unused for a long time. Bad fuel won’t burn properly, and it can cause your chainsaw to stall or not work at all.

Low octane gas includes higher ethanol levels that make it less durable than 89 octanes or higher. It becomes harmful for your chainsaw’s engine after 8 weeks of being left unused. It leaves sediments and gunk that clog your fuel filter, fuel lines or, even worse, the carburettor.

If you haven’t used your chainsaw for more than eight weeks and left fuel in it, try replacing the fuel. Use brand new 89 or more octane fuel and see if that works. If the fuel has been left for too long, your engine might be too affected to work properly. You can look at new Husqvarna chainsaws for sale so that you are sure the engine is working at its best performance.

Fuel Delivery Problem – Check the fuel filter and fuel lines

A clogged fuel filter will starve your chainsaw’s engine, and it can also damage it by letting contaminated fuel into the engine. Bad fuel can also clog the carburettor. Clogged carburettors are one of the most common reasons why a chainsaw won’t stay running or start at all.

If you haven’t used the chainsaw for a long time, it’s best to replace the fuel and fuel filter before using it again. Once you have drained the fuel tank, check the fuel lines. They are designed to be in contact with fuel, but because of time, or exposure to deteriorated fuel, they can get damaged. Most experts recommend avoiding ethanol gas, which is harmful to the fuel lines.

A simple guide to why your chainsaw keeps stoppingClogged Air Filter – Check the air filter

Your chainsaw’s engine needs the right supply of air to run properly. A clogged air filter can be the reason why your chainsaw won’t start or stay running. Find your chainsaw’s air filter and remove it. If it’s clogged or too dirty, wash it or replace it. Depending on your chainsaw’s model it will have a washable or a conventional air filter. Clean it or replace it and test your chainsaw.

Clogged Exhaust – Check the spark arrester

Chainsaws come with a spark arrester, which is a small screen that intercepts sparks from coming out of the machine. It’s a safety feature to prevent starting a fire, especially when you are working with flammable items such as wood and sawdust. It’s important especially because of the tension and speed of aggressive chainsaw chains. Exhaust fumes need to leave the engine without restrictions; otherwise, the engine will stall. Remove your chainsaw’s spark arrester to see if it is clogged or damaged. If it’s clogged, you can clean it with a wire brush, and if you see it too dirty or damaged, it’s better to replace it.

Clogged Fuel Tank Vent or Fuel Cap – Check the air vent

The pressure inside the fuel tank needs to match the atmospheric air pressure to allow the free flow of fuel to the carburettor. Most chainsaws fuel tanks have air vents for this matter; only a few models have vented fuel caps. You should check your motorized saw’s user manual to find where the vent is and how to clean it. If your chainsaw has a vented fuel cap, the job is much easier: you can try cleaning or replacing it. A quick test you can do is to loosen your chainsaw’s fuel cap, making sure that air is allowed into the tank. Now start your chainsaw very carefully. If it keeps running, the problem is the fuel tank venting. You can start working from there.

Never start or use your chainsaw without the fuel cap on!

Blocked or damaged Idle Port – Check the idle port

The idle port, also called idle screw, is used to adjust the airflow into the chainsaw’s engine. Oil, dirt, and debris can block them, preventing the air from flowing into the engine. If the idle port of your chainsaw gets blocked or damaged, your chainsaw won’t stay running.  Check the idle port for damage or blockage. If it’s blocked, you can clean it using alcohol, kerosene, or any solvent. If it’s damaged, you will have to replace it.

Bad Spark Plug – Check your chainsaw’s spark plug

A bad spark plug can prevent your chainsaw from starting and can cause your chainsaw’s engine to lose power and stop. This power loss may not be noticeable while your engine is idling or cutting softwood. But if your chainsaw’s engine stops when you are cutting harder wood, this could be the problem.

You can remove the spark plug and check it for signals of damage. Cracks on the porcelain insulator, carbon build-up at the electrode, or damage and excessive light in the electrode are things to look for. Having a spark plug tester handy is always helpful to check whether the spark plug is working and if the spark is strong enough. If you haven’t changed your chainsaw’s spark plug for a long time, it’s a good time to do so. Any internal combustion engine will run smoother and will have better fuel efficiency with sparkplugs in good conditions.

Clogged or Broken Primer Bulb / Checking the primer bulb

Some models have a primer bulb. If your chainsaw does have one, the primer bulb can be stuck with fuel and/or oil. Its material can crack due to exposure to the environment. The cracks allow air to escape, preventing a proper idle. If that’s the case, the primer bulb should be replaced.

More reasons why your chainsaw won’t stay running

The problems listed so far should be able to be fixed without professional help. Below, we are going to cover more complex problems that require more technical knowledge and expertise.

Your Chainsaw’s Carburetor Needs Calibrating – Adjust the idle, high, and low screws

Chainsaw service and repair CanberraAs the engine and its components wear out, the carburettor may need some adjustment. To do this, chainsaws come with 3 adjustment screws that are used to give the engine a proper airflow. Adjusting your chainsaw’s carburettor is not easy. Every model has specific settings and tuning an engine by ear is hard for an untrained person.

An engine stalls when it’s not getting enough or is getting too much fuel from the carburettor. Chainsaws have a screw to adjust the airflow when the engine is idling, when it’s running at low speed, and when it’s running at high speed.

If the chainsaw stalls while you are revving it up, or it doesn’t reach its full power, you need to adjust the high-speed screw. If your chainsaw’s engine stalls while idling, you need to adjust the idle screw. And if it fails at low speeds, you have to adjust the low-speed screw.

Bear in mind that while you are turning these screws, you are adjusting the air-fuel ratio of the engine. If you leave the fuel mixture too lean or too rich, it can be extremely harmful to your engine. That’s why it’s recommended to take your chainsaw to a service shop for this problem. Canberra Diamond Blade offer chainsaw service and repair and can help you out!

Compression Problems – Test your chainsaw’s engine compression

Maybe your chainsaw is old, had lubrication problems, hard to start, or you’ve noticed that before this problem it didn’t feel as powerful as usual. If so, you should do a compression test.

A healthy engine should have more than 70 PSI for a small saw, bigger engine saws should have at least 100 PSI. There are cheap compression tester gauges in the market. You can do it yourself or you can take your chainsaw to a specialized shop to have it tested. If your chainsaw’s engine has low compression, it’s a signal that there’s internal damage like bad piston rings, bad crankshaft seals or a cracked piston. Fixing these damages is expensive and they are a signal that maybe it’s time to buy a new chainsaw. That’s why it’s better to do a compression test before spending money on relatively expensive parts like a new carburettor.

Dirty, Clogged, or Bad Carburetor – Check your chainsaw’s carburettor

After you’ve made sure everything else is ok, it’s time to check the chainsaw carburettor. Clogged carburettors can cause an engine to stall or not start at all. You can try to clean it with a carburettor cleaner. If this fails, you can remove it for deeper cleaning. You can use an automotive carburettor cleaner to do the job.

If you have time and patience, you can buy a carburettor rebuilding kit. It has all the components that are usually worn out or get damaged plus a set of fresh gaskets and O-rings. Once you have cleaned and rebuilt your carburettor, it’s time to put it back and test your chainsaw. If it works, hurray. All your effort was worthwhile.

If it doesn’t work, your carburettor might be damaged beyond repair and that you need to replace it. When you are sure that the carburettor is the problem, maybe you would like to just go for a new one. It will cost you more, but it will be much faster and easier. If you replace the carburettor, remember to buy new gaskets for between the carburettor and the manifold. Replace the fuel filter and gas to give it a fresh and clean start.

Always check your chainsaw’s user manual. It provides important information about the parts that need regular servicing and other important instructions for the machine’s maintenance and your safety.

If you have more chainsaw questions, here at Canberra Diamond Blade, we are happy to help! In the meantime, check out our other chainsaw articles answering questions like if it’s worth sharpening a chainsaw chain. We have an 18-inch chainsaw detailed guide! Troubles with your lawnmower? Here’s a simple guide to troubleshooting your lawnmower.

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