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Starting a Chainsaw without a Primer Bulb. Tips from a Pro

If your chainsaw doesn’t start after several pulls and the primer bulb appears to be damaged, you need to install a new bulb before the saw can be started. But what if there was a way to bypass the bulb entirely? In this blog, I shall explain to you how to start a chainsaw without engaging the primer bulb.

Starting a chainsaw without a primer bulb.

A primer bulb aids in the cold starting of your engine. If it gets damaged, it can be bypassed simply by blocking the line which connects it to the carburetor. To start your chainsaw with a primer bulb, inject some starter fluid or gasoline through the air filter into the carburetor. Or you can pour it directly into the engine through the spark plug hole. After adding, pull the cord and check if it starts.

The following article gives a detailed explanation of how to start a chainsaw without a primer bulb. I will show how to bypass it and prime a chainsaw with no primer.

Do all Chainsaws have Primer Bulbs?

Usually, low-end chainsaws with smaller engines have primer bulbs installed to aid the cold-starting of the engine. Saws having engines larger than 40 or 50cc do not have this feature.

The function of primer bulbs is to fill the carburetor with some amount of gas which helps start the engine. Primer bulbs create a suction when they are pressed. The vacuum draws fuel from the tank and fills the carburetor with it. When the cord is pulled, this fuel is delivered to the engine, so combustion becomes sustainable. The engine starts as a result.

Another important function of primer bulbs is purging off the air trapped in the fuel line that connects the fuel tank with the carburetor. The air gets sucked out from the line and back into the fuel tank by pressing the bulb. Hence, the fuel flow to the carburetor gets easier. Due to this reason, primer bulbs are also called purge bulbs.

Engines larger than 40cc create enough compression in their piston cylinders that they do not need to be supplied with an additional fuel charge. Hence, no primer bulb would be needed in larger and high-end saws.

Primer bulbs were introduced for saws more suited for domestic use that are not used for longer intervals. Hence, a primer and a choke feature were needed to aid the starting of such machines. This helped start engines when temperatures were cold, and the saws weren’t as thoroughly maintained either.

Can you Run a Chainsaw without a Primer Bulb?

Chainsaws that have primer bulbs can be run without them in most cases. The goal is to supply the engine with some amount of gasoline so that the engine delivers enough power to start the chainsaw.

For some engines, primer bulbs are quite necessary as without them, the engine doesn’t produce enough power to start the chainsaw. In these engines, however, manual priming may help you start the chainsaw in case the primer bulb isn’t working.

To manually prime your chainsaw, you need to squirt some fuel or a carb cleaner liquid into the carburetor through the air filter. This additional fuel may help start your engine without a primer. In some cases, you can add additional fuel to the engine via the spark plug hole.

All these methods aim to ensure that the engine receives enough fuel to deliver the requisite power. When done manually, it may become a hassle as you would need to unscrew some parts every time while starting the chainsaw. Hence, if your device uses a primer bulb that has gone faulty, it would be a better idea to replace it with a new one.

How do you Bypass a Primer Bulb?

Bypassing a primer bulb is simple. Just disconnect the carb line and plug it with a ball bearing to seal it entirely. Then, connect it back to the carb. Ensure that any possible air leakage spots are dealt with properly.

Bypassing a primer bulb may seem like an option when you have work to do and can’t find a replacement bulb. Nevertheless, you can still start your chainsaw without a bulb, but if you intend to use it for the long term, I recommend installing a new primer bulb instead, as it would ease the starting procedure and be more convenient.

Still, bypassing a primer bulb on a chainsaw is quite easy.

  • Expose the lines: Unscrew the casing on the chainsaw to reveal the fuel lines that connect to the bulb.
  • Seal the carb line: The only thing that you need to do is to disconnect the hose linked to the carburetor. Insert a small ball bearing or any other object to perfectly seal that line.
  • Reconnect: Once sealed, connect the line back to the carburetor.

With the line removed, your bulb has been bypassed and fuel flows directly from the tank to the carburetor.

My Opinion:

Although you have successfully bypassed your primer bulb, now you would need to make more effort in starting your engine. I would recommend that you turn the choke lever at maximum setting as this would supply additional fuel to the engine. Plus, readjusting your L and H screws would further help start the engine despite the primer being out of the way.

Some users have found that shaking their chainsaw’s fuel tank builds some pressure in the tank and fills the carburetor with some fuel. This may also aid in starting your chainsaw after the bulb is bypassed. Please note that you would only need the primer to start the engine. Once it’s started, it wouldn’t need the primer anyway.

How to Prime a Saw with no Primer?

To manually prime a chainsaw, you need to inject some starter fluid into the engine through the air filter. In some cases, it may be added via the spark plug hole.

Equipment Needed:

For this procedure, you need starter fluid and a flat head screwdriver, and you are good to go. If a starter fluid is unavailable, make sure you use gasoline mixed with engine oil in 50:1parts instead.

Things to Consider:

Please keep in mind the following factors before you proceed:

  • Priming time: Depending on your skill level, priming the saw engine without a primer bulb could take anywhere from 5 to 20 minutes. If you’ve previously performed chainsaw repairs, it shouldn’t take you more than 5 minutes.
  • Starter fluid: A starter fluid is required for this kind of priming. The fluid is a mixture of chemicals that act as fuel and aid in starting the engine when it fails to prime.
  • Caution: Use the starter fluid cautiously and avoid spraying too much, which may cause blockage and disrupt the carburetor’s airflow.

● Step 1. Initial Checks:

Preparing the chainsaw for the task is usually preferable before starting the engine. This stage involves ensuring that all fuel lines and carburetor connections are correctly linked. Furthermore, the spark plug wire must be connected, and the spark plug must be in good condition. Check your gasoline tank to see if any fuel needs to be added.

You must now discover and investigate the problem with the priming bulb. It lies close to your carburetor/air filter assembly. It may be located beneath the carburetor in some models. The bulb is usually red or black.

Examine your primer bulb to check whether it is cracked or torn. If anything appears to be broken, that is why it does not work. If everything appears to be in order, press it three times to allow fuel to enter the carburetor and begin combustion.

– To start the engine, pull the cord:

This is an optional step that can be conducted to determine whether the engine starts with a bad bulb or not. After pressing the primer bulb three times, push the choke lever to the maximum position. Pull the cable at least three times to see if the engine starts.

● Step 2. Locate and Remove the Air Filter:

If your engine does not start after completing the above instructions, you should consider manually priming it with starter fluid. But first, we must remove the air filter from which the fluid must be sprayed. I suggest photographing the air filter assembly to assist you in keeping track of individual parts and know where to put them.

– Identify the air filter:

Finding the air filter is quite simple, as it is located on the side and can be easily be removed.

– Remove the air filter:

Take the air filter out of the housing. Ensure that the filter assembly is completely separated from the saw. Remove any nuts, screws, or retention pins connected to the chainsaw.

● Step 3. Spray the Starter Fluid:

Now you should spray the starting fluid into the air inlet. The air cleaner was linked to the engine at this location. Squeeze some starting fluid into the hole. Avoid spraying too much fluid, which could clog the jets and cause further issues.

Please note that as an alternative, you can also pour the starter fluid or gasoline into the cylinder head directly. This is done from where the spark plug is present. To do this, first, remove the spark plug boot. Then, remove the spark plug using a correctly sized wrench/socket wrench. Once the plug is removed, add a small amount of starter fluid through the hole.

● Step 4. Reconnect the Air Filter Assembly:

We’re ready to start the engine now that the addition of fluid is finished, but first, the air filter housing and filter must be reconnected to the engine. You should carefully place it back into the housing, fastening it as needed. You must complete this step as soon as possible. Otherwise, the starter fluid, which contains some fuel, may evaporate, and you may need to add it again.

● Step 5. Start the Saw:

After you’ve reassembled the filter and its housing, it’s time to start the chainsaw’s engine as usual. Pull the cable while the choke is set to the maximum setting. It might not start right away, so give it a few attempts.

If the fluid has not yet evaporated, it should start immediately. If it does not start, you may need to add the starter fluid again. If it starts following the fluid spray, you have effectively primed the engine without using the priming bulb.