Rajan Wilcox
When it comes to older Mercury outboards, the size of the fuel line you need depends on the engine's horsepower. A 5/16 fuel line is suitable for engines up to 115 HP, while a 3/8 fuel line is required for engines above 115 HP. It's important to use the correct fuel line size to ensure proper fuel delivery and avoid strain on the fuel pumps, which could lead to premature failure or damage to the engine. Mercury also offers pre-assembled fuel line kits that are EPA-approved and compatible with their outboards, ensuring compliance with regulations and optimal performance.
| Characteristics | Values |
|---|---|
| Engine Manufacturer | Mercury |
| Engine Horsepower | 50-90 HP: 5/16" hose |
| 90 HP: 3/8" hose | |
| 115 HP and above: 3/8" hose | |
| Hose Barb | Present where the fuel line hooks up to the engine |
| Hose Size | 3/8" |
| Ethanol Compatible | Yes |
| Approvals | EPA, CARB, ABYC H-25, and USCG |
| Inside Diameter | 3/8" |
| Outside Diameter | 11/16" |
| Length | 6 ft |
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What You'll Learn
5/16 fuel line for <115 HP engines
A 5/16" fuel line can be used for outboard engines with up to 115 HP. This size is commonly used for smaller outboards, such as kicker motors and sailboat outboard engines, as it fits easily into smaller rigging tubes. It is important to ensure that the connections are tight to prevent air leaks, which can cause the engine to lose prime and lead to rough running.
The 5/16" fuel line may not be suitable for engines above 115 HP, as they require a larger fuel line to meet the increased fuel demand. Using a smaller fuel line on a larger engine can strain the fuel pumps and potentially damage the engine.
It is recommended to check the hookup on the engine, as the size of the hose barb will indicate the appropriate fuel line size. If the connections are loose, it is advisable to change to a 5/16" hose or use an adapter to step down from a 3/8" line.
The 5/16" fuel line is suitable for a range of outboard engines, including those from manufacturers such as Mercury, Honda, Yamaha, Suzuki, and Johnson/Evinrude, as long as the engine's horsepower is 115 HP or lower. Ensuring the correct fuel line size is crucial for the safe and efficient operation of the outboard engine.
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3/8 fuel line for >115 HP engines
When considering the fuel line size for older Mercury outboard engines, it's important to ensure you have the correct parts for optimal engine performance and safety.
For Mercury outboard engines above 115 HP, a 3/8" fuel line is required. This is a general rule that applies regardless of the engine manufacturer, be it Honda, Yamaha, Suzuki, or Mercury itself. The 3/8" fuel line ensures that the engine receives the necessary fuel supply to meet the demands of higher horsepower.
Using the correct fuel line size is crucial to prevent potential issues. While a 5/16" fuel line may physically connect to an engine above 115 HP, it will not provide sufficient fuel flow, leading to strain on the fuel pumps and potential damage to the engine.
The 3/8" fuel line is compatible with a range of Mercury outboard engines. For example, it is suitable for Force 40 hp and larger (1993 and newer) and 9.9/15/25 hp (1998) engines. It is also compatible with all Mercury/Mariner outboards that utilise a clip-on type disconnect at the engine end and a 3/8" ID fuel line.
When purchasing a 3/8" fuel line for your Mercury outboard, look for marine-grade options that are weather and UV-resistant. Ensure that the product meets the necessary standards and regulations, such as USCG type B1-15 SAE J1527 and ABYC Accepted Standards.
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Mercury's silver fuel line
Mercury Outboards have varying fuel line sizes depending on the engine's horsepower. For a 50-90 horsepower outboard engine, a 5/16" fuel line is required. For engines above 115 horsepower, a 3/8" fuel line is necessary. For example, a 250 EFI engine will need a 3/8" fuel line.
When choosing a fuel line, it is important to consider the engine's specific requirements and the manufacturer's recommendations. The connections must be tight to prevent air leaks, which can cause engine problems. It is also crucial to ensure that the fuel line is the correct size for the engine to avoid strain on the fuel pumps and potential damage to the engine.
You can find Mercury outboard fuel lines and fittings from various retailers, including Amazon and Wholesale Marine. Amazon offers free shipping on eligible orders and provides a range of related products, such as fuel filters, connectors, and fuel tanks. Wholesale Marine allows you to find the right parts for your engine by selecting the engine manufacturer, part type, and model.
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EPA-approved fuel systems
The size of the fuel line for older Mercury outboards depends on the engine's horsepower. A 5/16" fuel line is suitable for engines up to 115 HP, while a larger 3/8" fuel line is required for engines above 115 HP.
Now, regarding EPA-approved fuel systems, as of January 1, 2011, the U.S. Environmental Protection Agency (EPA) and the California Air Resources Board (CARB) implemented regulations requiring all portable fuel systems manufactured for use with gasoline-powered marine engines to produce zero evaporative emissions. This means that all new portable fuel containers, including outboard motor fuel tanks, must be fully sealed to prevent gas vapors from venting into the atmosphere. As a result, these fuel tanks are designed with multiple layers to prevent the release of hydrocarbons, which can cause a build-up of pressure from gas vapors inside the tank.
To comply with these regulations, EPA-approved fuel systems feature several components:
- Fuel Demand Valve (FDV): This valve is installed along the fuel line between the fuel tank and the primer bulb. It prevents engine flooding by controlling the flow of fuel, allowing it to pass through only when demanded by the engine. FDV valves are compatible with all new EPA-compliant fuel tanks and can be purchased separately or as part of a fuel line assembly.
- Non-venting Cap: Unlike pre-2011 fuel tanks that had manually operated vents to release vapor pressure, EPA-certified tanks do not include this feature. Instead, they have a non-venting cap that helps maintain a sealed system.
- Multi-layered Tank Construction: EPA-compliant fuel tanks are designed with multiple layers to prevent the release of hydrocarbons and reduce evaporative emissions.
- Pressure Holding Capacity: EPA-certified tanks are required to hold a minimum internal pressure of 5 psi, which can be caused by ambient temperature changes or warming from the sun.
Upgrading to an EPA-compliant fuel system offers several benefits. Firstly, it helps keep your fuel contained within your outboard motor tank, preventing evaporation, spraying, or spilling. Additionally, the use of a Fuel Demand Valve can improve engine performance by ensuring a smooth flow of fuel and preventing engine flooding. While these EPA-compliant systems may cost more than their outdated counterparts, they contribute to a cleaner environment and help you avoid potential issues with your engine.
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Mercury's fuel line kits
Mercury Fuel Line Kits are available in 5/16" and 3/8" sizes. The 5/16" fuel line is perfect for smaller outboards, allowing for easy installation in a smaller rigging tube while still providing the proper amount of fuel to the engine. It is typically used for engines up to 115 HP. The 3/8" fuel line, on the other hand, is required for engines larger than 115 HP. It is worth noting that some older engines with lower horsepower may also require a 3/8" hose.
The Attwood Mercury Fuel Line Kit is a popular option that comes in both 5/16" and 3/8" sizes. This kit includes a fuel line, various fittings, a primer bulb, and optionally, a Fuel Demand Valve. The fuel line is designed to prevent kinking and hardening and is rated for temperatures up to 100°C. The kit is EPA-certified and compatible with Ethanol-blended fuels and all OEM-brand engines. It is a good choice for those seeking performance, safety, and value.
Mercury also offers their own fuel line kits, which include a fuel line, connector, and filter. These kits are available on Amazon and are eligible for free shipping. Additionally, Wholesale Marine and Land & Sea Supply carry a range of Mercury outboard fuel lines and fittings, providing customers with a variety of options to choose from.
When considering which fuel line kit to purchase, it is important to keep in mind the specific requirements of your engine. Factors such as engine manufacturer, horsepower, and fuel type can influence the appropriate choice of the fuel line. It is always best to consult the engine manufacturer's recommendations and seek out parts that are compatible with your specific Mercury outboard model.
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Frequently asked questions
A 5/16" fuel line is standard for smaller engines, while a 3/8" line is required for engines larger than 115 HP.
A 250 EFI will need a fuel line of at least 3/8".
A 90 HP engine requires a 5/16" hose.
A 50 HP engine will need a 5/16" hose.
Mercury's silver fuel hose is one of the best options, but make sure the fuel hose you choose is marked "SAE or USCG" approved.
