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.

The basics

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?

  • Yes: All good, next test
  • No: 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).

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
  • No: 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.

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
  • No: I see cracks. 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.

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. The issue is most likely coming from the line or the bulb that you just replaced. Need further testing
  • No: it is still soft. The issue is most likely coming from your engine because a new bulb and line has not made a difference. Need further testing

Fuel line and bulb

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.

  • Yes: All good, next test
  • No: 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.

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?

  • Yes: All good, next test
  • No: 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.

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.

  • Yes: 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.
  • No: All good, next test

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.

  • Yes: All good, next test
  • No: Air is getting into the fuel line either through the cracks or through a gap in the hose clamps.

Filter and engine

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.

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

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.

  • Yes: 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.
  • No: All good, next test

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