What Are The Symptoms of a Bad Primer Bulb?(Explained)

To start an engine, you need to prime it. Which means spraying gasoline inside the induction system of a piston engine.

A small bulb or a button that is pressed to prime the engine before starting is called the primer bulb. The bulb is generally made of rubber or other materials that are flexible.

One of the many reasons for not being able to prime the fuel is a bad primer bulb. In this article, I will discuss the symptoms to look out for when you have a bad primer bulb.

What Sign You Should Look for to Detect a Bad Primer Bulb?

Many issues come up when a primer bulb goes bad. Some issues resemble a bad fuel tank as well.

However, the most prominent sign of a bad primer bulb is the primer not getting hard. Before starting the engine, the primer bulb needs to be hard. But when it is bad, you may not be able to get it hard.

What Are the Symptoms of a Bad Primer Bulb?

With primer bulbs, sometimes the problem lies in other parts of the engine. A bad primer is a by-product of other problems. Here I will discuss the symptoms that directly indicate a bad primer bulb. As you go down, you will find other problems that indicate ‘why’ the bulb might not be working.

Some symptoms of a bad fuel pump are addressed below:

1. Primer Bulb Not Hardening

In a regular situation, shut off the motor. Check whether everything is hooked up normally with an open vent.

Now press the bulb, it is supposed to draw out the gas from the tank. This should continue until the carburetors are not getting feed due to carburetor float closing.

This is the point where the bulb should be hard. It should continue to remain so until the engine starts and it runs for a while. In between, you shouldn’t need to pump more.

But when you are running the motor, the bulb should not stay hard.

The primer bulb should lose hardness once the carburetor is filled. This is when fuel comes to action.

Now, this is the ideal situation. The primer bulb not getting hard in time points to fuel leak on the engine side. Primer bulb getting flat when fuel is running points to fuel restriction.

In no situation should the primer bulb stay hard at a higher RPM!

A change of the ideal situation points to a bad primer.

Check for any kind of leak or a carburetor issue as well.

2. Cold Start and Ticking

Check your fuel pump and fuel lines. Are all okay?

With everything normal, you shouldn’t have to deal with a cold start. Your engine should start smoothly and you shouldn’t have to prime repeatedly.

Moreover, you may hear a ticking sound, coming directly from your primer. Customers who face a bad primer issue have reported hearing the sound.

Right after they replaced the primer bulb, everything was okay.

3. Engine Losing Prime/Difficulty Priming

Notice if your engine is losing prime within 15-20 minutes of priming. Also notice when the engine’s been idle for a while, it needs re-starting. This duration may be for an hour or so.

Starting the engine without squeezing the primer bulb for dear life will be a problem. However, the engine may immediately start at squeezing the primer bulb.

Usually, people do a thorough servicing from the dealer in this case. But most of the time, it is a small issue of a primer bulb.

Check if your primer bulb is mounted in a vertical position. The orientation says that your primer is okay.

Then check the bulb. If it seems to have an unusual feel to it (hard when it should be soft) then that’s the problem.

4. Gas Pumps But Engine Shuts Off

Many times, a bad primer bulb pumps gas. Although it doesn’t harden enough.

In this case, the engine may not start often. Especially when your boat is in water.

There are two valves of a primer bulb. The inlet check valve and the outlet check valve. The engine doesn’t get enough power with problems in the valves.

Keep an eye out for this symptom too!

5. Leakage in the Fuel Lines

Many times, a primer bulb fails because of a fuel line leakage. This is why it’s hard to diagnose the major problem.

Check for a fuel line leakage. Lack of pressure in the fuel pump indicates fuel line leakage. The boat might suddenly plane out and die.

You may occasionally see bubbles of air coming out the lines.

A common problem is the needle valve seal is escaped by the fuel pressure. The allows fuel to leak into the carburetor.

The angle of your engine determines if this leakage escapes through the carburetor’s mouth.

Keep in check the diaphragm for leakages.

6. Vent Valve Problems

Vent valve problems cause a bad behaving primer bulb.

Take an air hose and blow the vent out. This will clean the valves.

If this doesn’t fix the primer bulb, then the issue may be any one of the above.

Be careful when cleaning the vents. You don’t want to blow out the primer bulb valves (inlet/outlet).

It’s best if you only check for clogged vents and take the boat for service.

How Should You React If You Detect a Bad Primer Bulb?

There’s not much you can do on your own if the issue is big. For example, if you have a bad fuel pump or fuel line. You can take the engine to the dealer to fix it.

If the issue is not something too serious, you can replace the primer bulb.

Additionally, you can replace the hose fittings around it. Make sure the clamps are fit tight.

The most effective fix that customers found was uprighting the primer bulb. Just vertically mount the primer bulb and squeeze. The bulb should get really firm before the engine starts.

Another trick to get the primer bulb hard is pinching the fuel line. Right before the engine and after the bulb. Pinch in that position and see if the primer bulb gets hard.

Is Replacing a Bad Primer Bulb Typically Expensive?

Replacing a primer bulb is typically inexpensive. You can find them on Amazon. Those cost around $12-20.

However, fixing the bigger issues that lead to a bad primer bulb can be costly.

How Often Should You Change the Primer Bulb?

The primer bulb is made of rubber and is affected by the sun. Changing the primer bulb every 4 years is optimum.

It definitely needs changing if the rubber gets too hard or black. Black color is caused by a leak.

Change the primer bulb if you see any of the mentioned symptoms in this article. But be careful of boxed bulbs that are available everywhere. Choose the original ones. Otherwise, it may not last even a season.

The Verdict

The primer bulb issue is a very simple one. It is more of an indicator for other major issues. Often this points to an engine going bad.

It is necessary to troubleshoot the issue as soon as possible. If not, many important problems may stay untended. This is bad for overall engine health.

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