How To Detect Air Leak in Outboard Fuel Line (Symptoms)

A fuel leak can happen for many reasons. But fixing up the fuel issue can take forever due to the issue not surfacing.

An air leak in the fuel line is not leaking air. Rather the air gets stuck for any reason and seeps out through misfires.

This article will help you to investigate the fuel issue in your boat due to an air leak. To find out how to troubleshoot this problem, read till the end of the article!

What Sign You Should Look for To Detect an Air Leak in Fuel Line?

In short, these are some signs;

  • Unusual air bubbles
  • Engine not starting or sneezing.
  • Not enough fuel gets pumped into the system.
  • The fuel in line could bleed back to the engine.
  • Starvation of fuel at the throttle.
  • The engine keeps losing prime.

What Are the Symptoms of an Air Leak in Fuel Line?

Here are some symptoms of air leak in the fuel line:

Slowly Dying Engine:

One of the symptoms of air stuck in the fuel line is a low-power engine. The engine will run rough. That is, it would turn fine, then start losing RPMs (Revolutions Per Minute).

The more the air is stuck, the more the engine is going to go slow.

More symptoms are: cutting out, sneezing, lack of power, or quitting.

Fuel Pipe Seems Softer:

As the air gets stuck inside the fuel line, the pressure decreases. This is why a stiff line seems to lose stiffness.

Bubbles in the Fuel Line

On the suction side of the fuel pump, bubbles can be visible easily when changed with a clear line.

Frequent Priming:

If you are constantly having to prime your fuel line, then it may be an air leak.

The primer bulb is located between the gas tank and the engine. It is used to fill the carburetor with fuel.

In priming, you fill the fuel tank, turning the engine stop switch off. You then turn the ignition key on. And turn the stop switch to ‘Run’. Continue until the pump stops and turn the switch off.

The suction of Gas:

An air leak can occur at a few specific places. One of the prominent places is between the fuel pump and the tank.

In this case, the air gets sucked into the tank instead of gas. This is called a ‘lean situation’. This is why enough fuel cannot get pumped.


The leaks that are found between the fuel pump and carburetor can create a fire. It may also create a complete disorder of the system.

Lack of Power to the Carburetor:

When air exists inside the fuel line, it gets sucked easier than fuel getting lifted. This results in a deficiency of fuel to the carburetor.

How Should You React If You Detect an Air Leak in Fuel Line?

Air Leak in Outboard Fuel Line Symptoms

As discussed before, air leaks can exist in different places. This is because you don’t know yet where your leak’s coming from. You can do the following things when you detect an air leak:

  • The quickest way is to suck out enough fuel so that the air leak comes out. Running the engine for 10-15 minutes without idle can do the trick. After that, check if the engine runs smoothly for a longer time. If there are no hiccups for 20-40 minutes, you have solved the issue.
  • Rebuild your carburetor connection up to the engine.
  • Establish new fuel lines and fuel pumps all the way up to the engine. This helps to get rid of invisible air leaks.
  • Check all the connections. Check for damage in any parts carefully. Replace damaged parts.
  • Check all the tubes, nozzles, plugs and every delicate part of the fuel pump, fuel line and fuel engine. You need to check for damage or corrosion. This might be leading air into the fuel line. Get rid of damaged parts immediately and rebuild.
  • You can tie nylon straps around fuel lines after purging out the air leak.
  • Check if the throttle and choke linkages are secure and properly working.
  • An air leak may still exist even after taking action. Don’t get professional help yet, get someone with a lot of patience. Someone who can handle the parts delicately.
  • Finally, check if pistons are alright as air leaks can cause damage to those. Check the entire system if possible.

Is Replacing a Fuel Line Typically Expensive?

Fixing a fuel line costs at least $120. But depending on the complexity and service charges, it can be from $750-1500.

Checking for fuel leaks is not literally a professional’s job. You need to stay persistent. Once you detect it you can replace the line.

In the case of replacing, you will require a professional. And judging by the range I wrote above; it is ridiculously expensive.

You can change it yourself. A good fuel line costs $6 to $7 per foot. You might also need to replace additional stuff.

Anyway, it will be a bit expensive if you go to replace things entirely.

How Often Should You Inspect or Service the Fuel Line?

Honestly speaking, you should check the fuel lines every time before fueling up. The rest of the time, replace them when you face problems.

Replacing fuel lines can be expensive. There is no exact duration after which you should change it.

Maintain engine health and fueling instructions properly. This way you will not get air leaks too often.

Final Thoughts

Air leakage is a simple yet irritating problem for many boat owners. From the continuous sneezing, misfiring engines to expensive measures of troubleshooting.

For this extra caution should be maintained at the time of putting fuel. Priming might help.

Sometimes air leak damages other parts of the engine as well, increasing expenses of fixing the issue.

Therefore, prevention of an air leak in the fuel line is the best way to keep air leak symptoms at bay.

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