7 Symptoms of an Air Leak in the Outboard Fuel Line

Air leaks in the fuel system of outboard engines aren’t all that uncommon. It’s a problem that plagues almost every type of outboard engine, with dire consequences in most cases.

An air leak in the fuel system will cause the engine to idle erratically or perform poorly. it might even cause dangerous out-of-line fuel spraying. It’s not easy to detect the air leak in the fuel system as it can only be noticed through performance. Yet there are a few telltale signs to deduce the same.

But that’s not all; what are these symptoms and their possible remedies? We detail it all in this comprehensive article.

What are the Symptoms of Having an Air Leak in the Fuel Line?

The symptoms of air leaks in the fuel line mainly depend on the type of outboard engine. Some might be petrol engines or diesel engines. 

Others can be gasoline or injected engines. We will include all the symptoms so that you understand the issue regardless of your engine type.

Symptom 1: Softened Fuel Pipe

The fuel pipe itself doesn’t become soft; rather, the pressure on the fuel pipe drops. 

In most outboard engines, the fuel pipe or fuel line is covered by a rubber or braided on the outside. It creates a hard structure with good fuel pressure.

If there is air buildup in the fuel, the line will not supply enough fuel. As a result, you will notice a softer fuel line to the touch. 

While it’s not the easiest to notice, it might be a symptom of an air leak if you see any crease or break on the line.

Symptom 2: Dying Engine

Another telltale sign of an air leak is the dying engine. How can you tell if an engine is dying? 

If the air builds up in the fuel line, the combustion unit will have an erratic supply. The result will be stuttered start and loss of RPM over the engine’s use. 

As the air leak becomes more severe, the engine will completely stop starting at one point.

Symptom 3: Presence of Prime

If you notice prime is the fuel line, chances are there has been an air leak. Prime comes from the primer bulb, and its main function is to ease the transfer of fuel to the carburetor.

The primer bulb is conveniently placed between the engine and the carburetor for ease of fuel transmission. If the prime leaks into the fuel, the air leak’s vacuum is primarily to blame.

Symptom 4: Lean Situation

It’s clear that an air leak might happen in the fuel line. But where does the leak happen exactly? Identifying where the leak happens is a good way to take recovery and prevention measures beforehand.

In outboard engines, the lean situation occurs when there is an air leak between the fuel tank and the fuel pump. The middle vacuum between the two points creates a lack of pressure. 

This lack of pressure, in turn, reduces the fuel flow to the ECU, resulting in an overall low performance and constant low fuel signal.

Symptom 5: Low Output from the Carburetor

The air leak might also cause a low fuel supply in the carburetor. Without a proper fuel supply, the output from the carburetor will dramatically fall. This is especially noticeable if the fuel supply is erratic.

In the early stage of the air leak, a complete vacuum doesn’t develop. As a result, you will notice an erratic performance. But with time, the carburetor will completely fail.

Symptom 6: External Fire

When you ignite the engine, there are chances that the fuel line might catch fire. It might sound scary, but this is also a definitive sign of an air leak in the fuel line.

The line between the fuel pump and the carburetor often builds up extra pressure due to the vacuum created by an air leak. 

This might create sputtering at the joining points. Fuel leaks out in small amounts from the sputtering. And that fuel might cause small fires externally.

Symptom 7: Presence of Bubble

This symptom is visible only if you remove the fuel line. On the suction side of the fuel line, you will notice a buildup of bubbles suggesting that air might have made its way to the fuel line.

Possible Causes of an Air Leak on the Outboard Fuel Line

When it comes to the cause of air leaks in the fuel line of the outboard, it’s just a handful. Here are three main ones from them.

  1. A leak in the engine oil system will eventually lead to a leak in the fuel line system. Since both the systems are connected in the outboard.
  2. The bumps and vibration while operating the outboard may cause the fuel, especially diesel, to leak out. This resulting leak may often trigger an air leak.
  3. The most common cause, however, is refueling. When filling up the tank, air might lodge in the storage, eventually making its way to the fuel line.

Replacement and Repair Costs of Air Leak in Outboard Fuel Line

Replacement and repair cost changes depending on several factors, but it consists of the cost of parts and labor. The table below shows the estimated cost of repairing the air leaks in the outboard fuel line.

ComponentCost (in USD)Service Charge (in USD)
Replacement fuel line60 to 12060 to 380
Bleeding air out of the tankN/A60 to 380
Replacement primer bulb30 to 3560 to 380

Tips for Maintaining the Outboard Fuel Line to Prevent Future Leaks

Here are a few quick tips for maintaining your outboard fuel line correctly to prevent leaks in the future.

  • Regularly check the engine oil level for possible vacuum
  • Inspect the entire outboard fuel line system for sputtering or fuel spraying
  • Regularly inspect the fuel color
  • Inspect the gas tank
  • Regularly service the fuel injector

Frequently Asked Questions

Now that you know everything there is about the outboard air leaks on the fuel line, let’s look at some of the commonly asked questions regarding the same.

Will the engine fail at full throttle because of air leaks?

Yes, there is a high chance that the engine will fail at full throttle if you do not address the air leak issue soon. The buildup of air over time will create a complete vacuum in the fuel line resulting in zero fuel supply.

Can I DIY air bleeding from the tank?

If you do not have professional training, it will be very difficult to bleed out the air from the tank on an outboard. It is better to get to a mechanic or service center for proper servicing.

Will the air remove itself from the outboard fuel line?

There is a common misconception that if you keep the engine running, the air will remove itself. That is not true for outboard because a vacuum will cause the engine to shut down. You must replace the fuel line or initiate an air bleeding procedure.

Do I need to replace the carburetor for air leaks?

No, you do not need to replace the carburetor for air leaks. In extreme cases, you might need to replace either the fuel line or primer bulb at best.

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