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Boat fuel line bulb or primer bulb won't get hard - Troubleshoot your engine

Our viewership consists of about 80% males above the age of 55, so let's steer away from the blue pill jokes about fixing something that won't get hard and get to right down to it. 

The primer bulb is located on the fuel line between the gas tank and the outboard (or inboard) engine. When you “prime the carburetor”, you are pushing fuel from the carb bowl to the barrel (using the bulb). Once there is gas in the barrel, it will easily be sucked into the cylinder of the engine. Therefore making starting the engine easier when it is called.

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Basic tests

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These tests are here to see if none of the basic things have been forgotten. We start with the tests that won't really cost anything and might tell you why you inboard or outboard fuel line bulb is not getting hard.
Test 
1

Is your fuel tank full, not tilted, with the vent opened?

We all forget the most basic things sometimes, so let's start there before anything else. Check your fuel tank and make sure it is not empty. Also, make sure that it is not on an angle when you are trying to prime it. Finally, is the tank vent open?
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Yes

All good, next test
Need further testing
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No

All good, next test
Your bulb is not getting hard because you're pumping air and the carburetor barrel is therefore not filling up with fuel. If your vent is closed, the fuel could be going up but then back down because of the venturi effect created in the tank (this would also indicate a malfunctioning bulb valve).
Your bulb is not getting hard because you're pumping air and the carburetor barrel is therefore not filling up with fuel. If your vent is closed, the fuel could be going up but then back down because of the venturi effect created in the tank (this would also indicate a malfunctioning bulb valve).
Need further testing
Test 
2

When you pump, are you pumping in a vertical position?

A primer bulb has a one way valve inside of it so the fuel that you pump won’t get back “down” the line and back into the tank. The way this valve works is with a moving ball that will block off the fuel. If you don’t hold the bulb vertically, you could prevent the ball from blocking the fuel.
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Yes

All good, next test
Need further testing
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No

All good, next test
The one way valve inside your primer bulb is not blocking the fuel from going back down, therefore fuel in the carburetor barrel is not accumulating and your bulb is not getting hard. We have added a video where someone cuts a bulb in half, you’ll understand.
The one way valve inside your primer bulb is not blocking the fuel from going back down, therefore fuel in the carburetor barrel is not accumulating and your bulb is not getting hard. We have added a video where someone cuts a bulb in half, you’ll understand.
Need further testing
Test 
3

Is the pickup tube inside the tank in working condition?

This is the tube inside the gas tank. It takes gas to the fuel line. If it is malfunctioning, you won’t be able to get fuel outside the tank. To check that, take the pickup tube outside the tank and inspect it. Look for cracks along the tube or at the base where it connects to the tank's cap.
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Yes

All good, next test
Need further testing
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No, I see cracks

All good, next test
Cracks on the pickup tube mean that when you pump the bulb, you are plumping air and not fuel, so your bulb will stay soft.
Cracks on the pickup tube mean that when you pump the bulb, you are plumping air and not fuel, so your bulb will stay soft.
Need further testing
Test 
4

If you pump using another tank, line, and bulb, what happens?

This test will determine if the issue comes from your outboard (or inboard) engine or not. Borrow another tank and fuel line and connect it to your engine, then press the new bulb. Is it getting hard now?
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Yes, it is getting hard

All good, next test
The issue is most likely coming from the line or the bulb that you just replaced.
The issue is most likely coming from the line or the bulb that you just replaced.
Need further testing
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No, it is still soft

All good, next test
The issue is most likely coming from your engine because a new bulb and line has not made a difference.
The issue is most likely coming from your engine because a new bulb and line has not made a difference.
Need further testing
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Fuel line and bulb tests

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Fuel lines and bulbs are made of plastic and are not always the most reliable equipment. Also, because the role of the bulb is to transfer gas in an air-tight hose, many of the issues related to an outboard (or inboard) primer bulb not getting hard can come from the bulb or the fuel line themselves. Let’s check that now.
Test 
5

Are the bulb and the line installed in the right direction?

The bulb has an arrow that needs to be pointing to the fuel line linked to the engine (not the tank's fuel line). In other words, the arrow points in the direction of the fuel flow. To inspect the fuel line, check if it is connected to the tank breather rather than the pickup tube, that could be it as well.
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Yes

All good, next test
Need further testing
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No

All good, next test
Because the bulb is installed upside down, the valve inside the bulb is preventing fuel from getting through. Also, if your line is not connected to the pickup tube of the tank, you are sucking air, not gas.
Because the bulb is installed upside down, the valve inside the bulb is preventing fuel from getting through. Also, if your line is not connected to the pickup tube of the tank, you are sucking air, not gas.
Need further testing
Test 
6

Are you able to prime the fuel line?

Priming a fuel line means that you made sure that there is no air in it. If there is, it will compress as you press on the bulb and gas won't get into the carburetor. To prime a tube, first disconnect the hose from the engine and cover its end with your thumb. Then, squeeze the bulb and as air gets out of the tube, your thumb should act as a one way valve. Can you get a strong stream of fuel out? Or is there nothing coming out?
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Yes

All good, next test
Need further testing
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No

All good, next test
If you cannot prime your line, this means your bulb or fuel line is most likely broken. Your bulb is not getting hard because gas is not getting to the engine.
If you cannot prime your line, this means your bulb or fuel line is most likely broken. Your bulb is not getting hard because gas is not getting to the engine.
Need further testing
Test 
7

Is the bulb old, has cracks, or small holes?

Bulbs unfortunately do not last very long. If the bulb is old, its check valve could be broken. Also, inspect it for cracks and small holes because this piece of equipment needs to be airtight.
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Yes

All good, next test
If your bulb is old or looks like it could let air through, there you have it. Also, the valve inside the bulb could be letting the gas go back down.
If your bulb is old or looks like it could let air through, there you have it. Also, the valve inside the bulb could be letting the gas go back down.
Need further testing
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No

All good, next test
Need further testing
Test 
8

Is the hose without cracks, and are the clamps tight?

As with the previous test, air leaks along the fuel line could also keep your engine from priming and your bulb from getting hard. Inspect the hose itself for signs of cracks (bend it gently at different points to make sure you are checking even the smallest cracks). Also check the tightness of the clamps (what links the hose to the bulb, the tank, and the engine), air could get through there.
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Yes

All good, next test
Need further testing
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No

All good, next test
Air is getting into the fuel line either through the cracks or through a gap in the hose clamps.
Air is getting into the fuel line either through the cracks or through a gap in the hose clamps.
Need further testing
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Filter and engine tests

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We enter a more complex set of tests. Now that we have looked at things related to the tank, the line, and the bulb, it is time to inspect the filter and the engine. One of these could be the reason why your bulb is not getting hard (for both inboard or outboard motors).
Test 
9

Is there fuel or air in the water separator?

This could be an issue only if your bulb is between the tank and the filter. Inspect air and water separators. Is there anything else other than fuel in there? If there is air in it, this could be the reason why you are having trouble priming your engine and getting your bulb hard.
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Yes

All good, next test
You are pumping gas but the gas just compresses some air in the separator, not pushing fuel all the way to the engine.
You are pumping gas but the gas just compresses some air in the separator, not pushing fuel all the way to the engine.
Need further testing
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No

All good, next test
Need further testing
Test 
10

Do you have a stuck float inside your carburetor?

A carburetor float is literally a floater inside the carburetor bowl. It regulates how much fuel enters the float chamber. It will block when a certain fuel level is reached and prevent flooding the engine. If you have a stuck float, you will have rich exhaust and your engine would regularly flood. If you have good technical skills, you can also open your carb and inspect the flow, we added a tutorial for that below.
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Yes

All good, next test
Your float is not blocking the fuel once the carb is full, therefore, you can pump and pump and you will flood your engine, and your bulb wont get hard.
Your float is not blocking the fuel once the carb is full, therefore, you can pump and pump and you will flood your engine, and your bulb wont get hard.
Need further testing
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No

All good, next test
Need further testing

You have not found your problem or maybe you need something else?

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Top questions about bulbs not getting hard

What is the purpose of a primer bulb?

The primer bulb is here to manually fill the carburetor barrel with gasoline when you want to start your engine cold. After you press it, a vacuum is created and gas will be drawn into the intake fuel line all the way to the carburetor. A one way valve present inside the bulb prevents gas from going back down the hose.

Where is the primer bulb?

The fuel line bulb is located between your gas tank and your engine. If you have a fuel filter (water separator), it will most likely be located between the filter and the engine, in other words, down-flow from the filter.

Is the primer bulb supposed to stay hard?

Yes. Because the part of your engine from the tank to the carburetor is an air-tight system, it should get hard when you pump and stay hard for at least an hour. If it does not stay hard when primed, it means you have a leak, check the test above to find where it is. 

How do I know if my primer bulb is bad?

If you think your primer bulb might be bad it is probably because you cannot prime your engine (send fuel to the carburetor when starting cold). This issue can have multiple causes. It could be an issue with the gas tank, the fuel line, the engine, or the bulb. To know if the issue comes from the bulb, check this article’s tests, specifically number 2, 4, 5, and 7.

I have to pump a primer bulb to keep the outboard running, why is that?

This might be because your carb bowl is not filling up as fast as you are consuming fuel, and you need to pump the primer bowl to keep the engine running. This could be because the tank is not sending gas fast enough. Check the pickup tube, fuel line, bulb, and water separator if any of them is clogged. If that’s not it, you might have an engine issue.

Outboard primer bulb goes soft, why is that?

Once primed, your bulb will slowly start to go soft once your engine is running. It is the case because the pressure that has built up between the bulb and the carburetor (thanks to pumping the bulb) will start to decrease as fuel is being consumed by your engine. If you bulb goes soft as soon as you stop priming, then you might have a leak and you should check the tests in this article.

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