Replacing Fuel Lines: Johnson 90'S Step-By-Step Guide

Changing the fuel line on a 90 Johnson outboard motor is a maintenance task that boat owners may need to perform from time to time. The fuel line is responsible for delivering fuel from the tank to the engine, and ensuring the correct fuel line size is crucial for the engine's performance and safety. The Johnson 90 hp engine typically uses a 3/8 fuel line, which is required for engines above 115 hp. However, some owners have reported using a 5/16 fuel line without issues, as long as the engine is not running at wide-open throttle, which could strain the fuel pump. When changing the fuel line, it is important to ensure tight connections to prevent air leaks and engine problems. Additionally, fuel hoses have different ratings and specifications for safety, including A1, A2, B1, and B2, depending on their use and location above or below the deck.

Fuel line size

The fuel line size for your Johnson outboard engine is important as it affects the engine's performance. If you have a Johnson outboard engine with more than 40 horsepower, a 3/8-inch diameter fuel line is required. This is because higher horsepower engines demand more fuel flow, and a smaller diameter fuel line will restrict the fuel flow, leading to insufficient fuel supply and potential damage to the engine.

For a 90 hp Johnson engine, a 3/8-inch fuel line is generally recommended. However, some owners of 90 hp Johnson engines have reported using a 5/16-inch fuel line without any issues. It is worth noting that the fuel line size may vary depending on the specific model and year of your Johnson outboard.

The fuel line size also depends on the engine's configuration. If you are running a V6 engine, a 3/8-inch fuel line is necessary. The size of the fuel line can also be determined by looking at the hose barb where the fuel line connects to the engine. The hose barb will be sized for either a 5/16-inch or 3/8-inch hose, and you should use the corresponding size fuel line.

It is important to ensure that the fuel line connections are tight to prevent air leaks, which can cause the engine to lose prime and run into performance issues. If you are experiencing air leaks or the fuel line is too loose, you may need to install an adapter to step down from a 3/8-inch to a 5/16-inch line.

Additionally, it is crucial to consider the type of fuel hose used. There are different specifications for fuel hoses depending on their application and location on the boat. Hoses with different US Coast Guard ratings, such as A1, A2, B1, and B2, are used for fuel lines above or below the deck of the boat.

Fuel pressure problems

If you're experiencing fuel pressure problems with your 90 Johnson, there are a few potential causes. Firstly, check that your vented gas cap is open and functioning properly. An inadequate vent could be causing a vacuum in the tank, preventing fuel from entering the line.

If your vented gas cap is functioning correctly, the issue could be related to the fuel line size. Ensure that you are using a 3/8" fuel line, as this is the recommended size for the 90 hp Johnson outboard. Using a smaller fuel line could result in insufficient fuel delivery to the motor.

Another potential cause of fuel pressure problems is an obstruction in the fuel line or at the pickup tube. To check for obstructions, remove the fuel filter and blow through both ends to ensure there are no blockages. If the filter is clear, reinstall it and check the pulse hose for any lack of fuel discharge, which could indicate a faulty diaphragm or fuel pump check valve.

If your engine is hard to start, it could be due to a clogged flame arrestor, a fouled spark plug, a drained battery, or old fuel. Ensure that your flame arrestor is clear of debris, your spark plug is functioning properly, and that you have fresh fuel in the tank.

Additionally, if your engine is equipped with a mechanical fuel pump, the diaphragm may be worn out or damaged, causing performance issues or a complete loss of pressure. Inspect the fuel pump for any signs of damage or leaks, and replace it if necessary.

Finally, if you are using ethanol fuel, consider switching to ethanol-free gas as it can lead to more problems with your fuel system.

Fuel hose fittings

When it comes to fuel hose fittings for a 90 Johnson outboard motor, there are a few things to consider. Firstly, it's important to ensure you have the correct hose size. For a 90 hp Johnson engine, the fuel line on the motor is typically 3/8", while the fuel line from the gas tank is often 5/16". However, some people choose to stick with the 5/16" fuel line, especially if the engine is not a V6, as this size is sufficient for fuel supply.

Now, let's discuss the fittings themselves. You'll want to look for fuel hose fittings that are compatible with your Johnson outboard motor. These fittings are designed to securely connect the fuel hose from the tank to the motor, ensuring a tight seal to prevent leaks. There are a variety of options available:

Types of Fuel Hose Fittings:

• Barbed Fittings: These fittings feature small ridges or barbs that grip the inside of the fuel hose, providing a secure connection. They are commonly used in fuel systems and are available in various sizes, such as 5/16" and 3/8". Barbed fittings are typically made of durable materials like acetal, which can withstand leaded, unleaded, and alcohol-blended fuel.
• Clip-Style Fittings: Johnson/Evinrude engines often use clip-style fittings, which employ a two-prong or spring-loaded clip mechanism to securely attach the fitting to the fuel hose. These fittings are available in sizes like 5/16" and 3/8".
• Bayonet-Style Connectors: This type of fitting uses a bayonet-style attachment, similar to those found in some light bulbs. They are available in sizes like 3/8" and come in male and female versions to accommodate different connection needs.
• Tank and Engine Connectors: Depending on your setup, you may need specific connectors for the fuel tank and engine. For example, you can find male tank connectors with 1/4" NPT (National Pipe Thread) that thread into the fuel withdrawal on the tank. On the other hand, female engine connectors with 3/8" hose barbs are designed to attach to the fuel hose on the engine side.

When purchasing fuel hose fittings, it's important to ensure they are compatible with your specific Johnson outboard motor model and fuel hose size. Additionally, always follow the manufacturer's instructions for proper installation and maintenance to prevent leaks and ensure the safe operation of your boat.

Fuel tank venting

If you are experiencing fuel pressure problems with your Johnson 90 hp outboard engine, there could be a few reasons for this. Firstly, it is important to note that the fuel system is not a pressurized system. The tank must be vented to allow for the displacement of used fuel with air. If the tank is not vented properly, it can create a vacuum that affects fuel delivery to the engine.

If you are experiencing issues with the primer bulb collapsing, there are a few potential causes. Firstly, check that the bulb is installed in the correct direction, with the arrow pointing towards the motor. If the bulb is installed correctly and still collapses, there may be a restriction in the fuel line. This could be due to an obstruction in the line or at the pickup tube, a vacuum from an inadequately vented tank, or a faulty bulb.

To troubleshoot fuel pressure problems, try the following:

• Check the vented gas cap to ensure it is open and functioning properly.
• Ensure that the fuel line is the correct size and not too small, as this may affect fuel delivery to the motor.
• Inspect the fuel line and pickup tube for any obstructions.
• Try using a portable and vented tank to isolate the issue to the tank.
• Consider bypassing the bulb after starting the engine to see if that makes a difference.

If you are still experiencing fuel pressure problems, it may be necessary to consult a marine mechanic or a Johnson outboard specialist for further diagnosis and repair.

Fuel line connections

When changing the fuel line on a 90 Johnson, it is important to consider the size of the fuel line, the type of fuel hose, and the connections to the engine.

The fuel line size for a 90 hp Johnson engine is typically 3/8". However, some older models may have a 5/16" fuel line. It is recommended to use a 3/8" fuel line for engines above 115 hp to ensure adequate fuel flow and prevent strain on the fuel pump.

There are different types of fuel hoses, and it is important to use the correct hose for your application. Below-deck hoses, or A1 hoses, are used for feeding fuel from the boat fuel tank to the fuel filter bracket or the engine. These hoses have a fire-resistant covering and are designed to have fuel in them at all times. A2 hoses are used for the fuel tank vent hose below the deck and are not meant to have fuel sitting in them. B1 hoses are similar to A1 hoses but are used above the deck and do not have a fire-resistant covering. B2 hoses are used for the fuel tank vent hose above the deck and do not have a fire-resistant covering.

When connecting the fuel line to the engine, ensure that the connections are tight to prevent air leaks. Loose connections can cause the engine to lose prime and run poorly due to air being sucked into the fuel line. It is also important to use the correct fittings and clamps for your fuel line size. Attwood makes fuel hose fittings specifically designed for Johnson/Evinrude/OMC brand engines and tanks, with barbed fittings for 3/8" or 5/16" fuel lines.

Frequently asked questions