How Does a Primer Bulb Work on a Chainsaw? A Guide

how does primer bulb work

Have you ever noticed how frustrating it is when your chainsaw engine starts to take longer than usual to operate? It occurs when an engine is left idle over an extended period of time with nearly evaporated fuel in the carburetor. The carburetor priming bulb fills that role.

The priming bulb’s job is to make sure the carburetor has enough brand-new fuel to start the engine smoothly. However, a priming bulb’s operation is more complex than you would realize. Now, without further ado, have a look.

How Do Primer Bulbs Work?

how does primer bulb work

Every chainsaw user should be aware of the answer to this frequently asked question in order to better grasp how a chainsaw functions. A small, round, perforated rubber or plastic button known as a priming bulb is used to draw fuel system  into a carburetor. Numerous tiny engines, including those in lawn mowers, tillers, and other outdoor power equipment, contain it.

The priming bulb enables the operator to inject a little amount of fuel system into the carburetor to start the engine when it is not running. The priming bulb is not used after the engine has been started.

A tiny check valve on the primer bulb restricts the flow of fuel to one direction only. When the priming bulb is depressed and fuel is fed into the carburetor, the check valve opens gas tank . The check valve closes after the primer bulb is removed, preventing fuel from pouring back into the bulb. It is the way the priming bulb operates! 

There are several potential causes for the primer bulb to not be functioning. The check valve’s malfunction is the most frequent cause gas tank . A broken gasket or a clogged check valve may bring it on.

The fuel line being obstructed is another typical cause of a priming bulb failing. A clogged gasoline filter or a kink in the fuel line are two potential causes. The engine won’t start if the priming bulb is broken. To resolve this issue, you must either clean or replace the priming bulb.

Different Primer Bulb Types for Chainsaws

Therefore, there are two different types of priming bulbs available in the market that safe place are employed in chainsaws. 

Snap-in Primer Bulb

A priming bulb with a snap-in construction may be quickly fitted to and removed from the chainsaw’s gasoline tank. The manner the priming bulb fastens to the gasoline tank accounts for safe place the “snap” in the name. It’s like putting two puzzle pieces together!

A snapping sound indicates that the priming bulb is locked into place as you insert it into the fuel tank’s hole. When using the snap-in style, you may quickly and simply change the priming bulb suction  if necessary. The engine may run badly or not start at all if they are placed incorrectly and allow air into the fuel tank.

Screw-in Primer Bulb

As the name implies, it screws into the gasoline line between the tank and the carburetor or the body of the carburetor. The screw-in priming bulb has a different attachment method but suction performs similarly to the snap-in primer bulb.

Because of their superior toughness and long lifespan, they are primarily utilized in chainsaws used by arborists and millers in the industry.

Do I Need a Primer Bulb?

Although a priming bulb is not strictly necessary for a chainsaw to operate, the excess air following two arguments should persuade you to have one:

Delivering fuel flawlessly

Fuel is efficiently delivered to the carburetor with the aid of a chainsaw priming bulb. Without a priming bulb, the carburetor might not get the gasoline it needs to drive the engine, which could cause poor performance and even harm to the engine itself.

A priming bulb can also aid in avoiding engine flooding. When there is too much fuel in the carburetor, the engine may excess air flood. Starting will be challenging as a result, and the engine could get hurt. The proper amount of gasoline is added with the aid of the primer bulb, lowering the likelihood of flooding.

Engine Start in a Moment

Time is money for arborists, and a chainsaws fuel tank  that starts slowly or generates a lot of noise can frustrate them and slow down their work. This problem is eliminated from your life with a priming bulb.

In cold weather or when the chainsaws fuel tank  has been idle for some time, it makes starting the engine considerably easier. Remember that one of the chainsaw’s most crucial components is the priming bulbs. It is a tiny, round, black rubber bulb that aids in providing the engine with the proper amount of fuel. Your chainsaw won’t small amount start or function correctly without it.

You are aware of how challenging it can be if you have ever attempted to start a chainsaw without a priming bulb. After a few damage seconds, the chainsaw will sputter and shut off. It is because of the carburetor not difficulty receiving enough fuel.

The carburetor gets the proper amount of fuel thanks to the priming bulb. It also aids in avoiding chainsaw stalling. You can difficulty still start debris your chainsaw if it doesn’t have a priming bulb, but it won’t run as well. If the priming bulb is broken or missing, it is recommended to replace it.

How Can I Tell Whether My Primer Bulb Is On?

There are three simple ways to determine whether the priming bulb on your debris chainsaw is damage functioning:

  • Check to see if you can still squeeze it. You should be able to see it reverting to its previous shape when you press it. And only when it is hard and firm is that possible. If it isn’t, that shows that insufficient pressure is being generated to force fuel into the carburetor.
  • The line pipes and primer bulb shouldn’t have any fractures, holes, or cracks in them. Fuel can escape from the system when there are leaks, which makes it challenging for the engine to start and function effectively.
  • Launch the vehicle! See how it functions. The priming bulb is probably doing just fine if the engine starts up and runs smoothly. However, if the engine struggles to start or runs poorly, it may show a problem with the priming bulb.

By the way, you can also test the primer bulb’s functionality by removing the carburetor’s gasoline line and pressing it. 

Symptoms Of A Bad Primer Bulb

Your chainsaw will have trouble starting if the priming bulb is defective. The following are signs of a faulty priming bulb:

  • The priming bulb inflates the fuel tank and pushes fuel into the combustion chamber through the carburetor. If your chainsaw won’t start, a blocked priming bulb may be the culprit. As a result, when the primer is malfunctioning, you may experience both problems, such as the chainsaw starting slowly or not at all.
  • A defective primer bulb will be difficult to press or won’t stay inflated, which are both clear symptoms of the problem.
  • Two typical signs that your chainsaw needs to be bypassed are the outboard primer bulb losing pressure and the inboard primer bulb leaking.
  • Primer bulb cracks might develop over time. Only one or two years are allowed for the primer to be utilized. After then, it will either crack or become damaged, thus you must replace it!
  • One potential issue with chainsaws is that the primer bulb could stop working if you feel gas releasing from the carburetor when priming the outboard motor. If this occurs, starting the chainsaw won’t be simple.
  • You can try bypassing the bulb to solve this problem if your chainsaw has air in the priming bulb.
  • The outboard primer bulb not getting firm is the other issue you have. The primer bulb not getting firm is one of the most frequent problems with small engines. This can be brought on by a number of various factors, but most frequently, the engine is simply not receiving enough gas. Make sure the gasoline line is not kinked by checking it.

It’s time to swap out the priming bulb if you experience these symptoms.

Can a Chainsaw Be Operated Without a Primer Bulb?

The priming bulb is used to supply the engine with enough gasoline. The engine, which also enables it to start powers the chainsaw. A priming bulb is present in several chainsaws. These saws can be started even without a priming bulb.

However, many chainsaws require a priming bulb to start. These chainsaws’ engines don’t have enough power to start up. Because of this, starting such engines may require manually priming them if the primer bulb malfunctions.

You must use an air filter to prime your equipment before adding gasoline or carb cleansing liquid to the carburetor. The engine, which the fluid aids in starting started your chainsaw. Through a spark plug hole, chainsaw users frequently need to supply extra fluid to the engine.

A priming bulb makes sure that there is enough fuel in the chainsaw and that it will have the power to start the engine. This task can be completed manually. But because you have to unscrew a few parts, it could be stressful for you. Fuel primer bulb replacement will be a better choice if the gas primer bulb isn’t operating.

Are Primer Bulbs Required for All Chainsaws?

Primer bulbs are common in low-end chainsaws. The chainsaw engine can start cold thanks to these LEDs. Larger engines, including those between 40 and 50 CC, do not, however, have such characteristics or components. There is no need for a priming bulb because an engine of at least 40 cc can readily generate adequate compression in the piston cylinder.

A chainsaw primer bulb’s function is to provide a little amount of gas into the carburetor, which aids in starting the chainsaw motor. The fuel is delivered from the tank to the carburetor with the aid of a vacuum created when the chainsaw priming bulb is depressed. When the user pulls the chainsaw cord, fuel is sent to the engine. The gasoline assists in starting the chainsaw and promotes sustainable burning.

This primer also serves the purpose of removing air bubbles that have become stuck in the fuel line that runs between the fuel tank and the carburetor. As a result, trapped air bubbles return to the fuel tank when you press the chainsaw priming bulb. In this manner, the flow transfer to the carburetor is made simpler. For your chainsaw, it can be a little difficult if the priming bulb won’t inflate. A chainsaw priming bulb is also referred to as a purge bulb for this reason.

These chainsaws, which are typically used for residential purposes but are no longer in use, contain the priming bulb. Because of this, these chainsaws added the priming to help the tool start. When it’s cold outside, the primer makes starting the engine simpler.

How Do I Get Rid Of The Chainsaw’s Primer Bulb?

Chainsaw priming bulbs may easily and simply be bypassed. The carburetor line needs to be disconnected, attached to a ball bearing, and thoroughly sealed. Reconnect the fuel line to the carburetor now, and you’re done.

There won’t be any leaks as long as the priming bulb fuel line routing is entirely secure! If your chainsaw has a priming bulb, you might wonder how to remove it. Here is a brief manual.

Exposing fuel lines

To expose the fuel lines, you must first detach the chainsaw’s casing. The fuel lines that are attached to the bulb will be exposed.

Carburetor line seals

 The pipe connected to the carburetor must be unplugged. The tiny ball bearing can seal that line. Besides a ball bearing, any additional item will work to perfectly seal the line.


 After properly sealing the fuel line, just reattach the fuel line to the carburetor.

You’ve avoided the priming by taking out the bulb. Fuel will flow directly from the tank to the carburetor as you use the chainsaw.

If you can’t find a replacement for the priming bulb on a chainsaw, bypassing it looks like a great solution. The chainsaw can still be used even if the fuel bulb won’t prime. But if you want to use your chainsaw for a long time, running it with a priming bulb is advised. Install a new priming bulb in the chainsaw to achieve this.

Final Word

The chainsaw’s priming bulb forces air into the carburetor, allowing the fuel and air to mix. However, there can be an issue with the chainsaw primer bulb even if the primer bulb is forcing air into the tank but the chainsaw won’t start. So if you want to avoid this problem and use a chainsaw without a priming bulb.

The primer bulb aids in the cold start of the engine by forcing air into the tank. However, if the chainsaw priming bulb suddenly stops working when you are busily sawing wood, you could be unable to finish your task. As you are in the middle of a forest, it may seem hard to replace the broken chainsaw primer bulb, but it is actually simple to bypass the primer bulb.

If you don’t know how to get around the chainsaw’s priming bulb, it’s not as tough as you may imagine. By obstructing the pipe that connects the carburetor and priming bulb, you can avoid using the primer bulb! After getting around the bulb, you can use your tool normally and carry on with your work!


Can You Repair A Primer Bulb’s Hole?

Yes, you can repair the hole in a priming bulb. A rubber patch and some super glue are all you need. Rubbish alcohol should be used to first clean the vicinity of the hole. In order to cover the hole, first cut a small piece of rubber off the patch. The rubber should then be covered with a thin layer of super glue and left to dry. Now your priming bulb ought to work like new!

What prevents a chainsaw’s primer from priming?

Your chainsaw primer may not be working for several reasons. If you recently replaced the fuel lines, there can be an issue with how the new lines were installed. If the chainsaw has been idle for a while, the priming might have gotten clogged and stopped operating correctly. It’s crucial to make sure the priming works properly if your chainsaw is having trouble starting.

Is There A Hole In A Chainsaw Primer Bulb?

Between the fuel tank and the engine is where the chainsaw primer bulb is located. The carburetor is fueled when the engine is started. A hole in the vented priming bulb affects the air/fuel mixture getting to.

Why Won’t My Chainsaw Primer Bulb Fill?

Your chainsaw priming bulb may not fill up for a few different reasons. The gasoline line being clogged is the most frequent cause. Fuel cannot be drawn from the tank and into the chainsaw priming bulb if the fuel line is kinked. The fuel filter may be clogged, which is the other possibility.

What Causes My Chainsaw Primer Bulb To Not Fill With Gas?

You can check a few things to figure out the issue if your chainsaw priming bulb isn’t gassing up. First, minute holes in the rubber may let air in and prevent adequate fuel from entering. As a result, carefully inspect it after removing the chainsaw priming bulb.

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