Understanding USCG Type A1, A2, B1 and B2 Fuel Hose

Marine fuel hose classifications describe both fuel permeation performance and, for Type A hose, fire resistance.

The "1" and "2" Matter

Under the traditional USCG definitions, Class 1 hose has a lower permitted permeation rate than Class 2 hose.

This is why A1 and B1 are typically associated with fuel-feed applications, while A2/B2 are more commonly associated with certain fill or vent applications.

Type A Adds Fire Resistance

The major distinction between A and B is that Type A hose must also satisfy the applicable USCG fire test.

That additional protection is why Type A1 is commonly specified in permanent and enclosed fuel-system applications.

Where Does USCG Type A1 Have to Be Used?

Under federal recreational-boat fuel-system rules, hose between a fuel pump and carburetor must be Type A1.

Hose from the fuel tank to the engine must be Type A1, or Type B1 only when the specific drainage limitation in the regulation is satisfied.

Fill and vent lines have their own A1/A2 and limited B1/B2 provisions. This is why "above deck" and "below deck" should be treated as useful selection shortcuts rather than the complete regulatory test.

What About A1-15 and Modern EPA Fuel Hose?

Modern marine gasoline fuel systems are also subject to EPA evaporative emission standards. EPA-certified nonmetal fuel lines are required to meet substantially lower permeation limits than the older USCG Class 1 definition.

When replacing newer fuel-system components, inspect the markings on the original hose and replacement hose. Current hose may include EPA-compliant or low-permeation markings in addition to the familiar USCG A/B classification.

Pro Marine Fuel Hose Size and Clamp Chart

Marine Primer Bulb Guide

A primer bulb is a small hand-operated pump installed in an outboard fuel line. Internal one-way valves allow repeated squeezes to draw fuel from the tank and move it toward the engine.

Which Direction Does a Primer Bulb Go?

The arrow on the primer bulb should point toward the engine.

Does a 1/2" Fuel Line Use a Primer Bulb?

Normally, no. A 1/2" fuel supply line generally indicates a larger, higher-flow fuel system where an inline hand primer bulb is not normally part of the system design.

Ethanol-Blended Gasoline and Marine Fuel Systems

Ethanol-blended gasoline deserves special attention in boats because marine fuel systems often sit unused for longer periods and operate in a moisture-rich environment.

Ethanol and Water

Ethanol is hygroscopic, meaning it can absorb water. Water can enter a boat's fuel system through contamination, condensation and normal exposure to the marine environment.

If enough water accumulates, the ethanol/water portion of the fuel can separate from the gasoline. This is commonly called phase separation.

Ethanol Can Loosen Existing Deposits

Ethanol is also an effective solvent. When introduced into an older fuel system, it can loosen gum, varnish and debris that accumulated in tanks and fuel lines.

That material can then travel downstream and contribute to clogged filters, carburetor passages or fuel injectors.

Ethanol and Older Fuel Hose

Older hoses that were not designed for alcohol-containing fuels may deteriorate when exposed to ethanol.

Possible signs include:

• Soft or swollen hose
• Hard or brittle hose
• Cracking
• Fuel seepage
• Loose hose-to-fitting connections
• Interior hose deterioration

Do not assume an old hose is safe simply because the exterior still looks acceptable.

Good Fuel Practices for Boats

• Buy fuel from a station or marina with high fuel turnover.
• Use the ethanol level approved by your engine manufacturer.
• Never use E15 in a recreational marine gasoline engine.
• Keep water out of the fuel system whenever possible.
• Use a properly sized fuel/water-separating filter where specified.
• Inspect fuel lines, primer bulbs and fittings regularly.
• Replace deteriorated or questionable hose.
• Use fuel stabilizer when appropriate, especially before storage.
• Do not expect an additive to repair damaged hose or restore severely stale fuel.

Tygon Fuel and Oil Hose Guide

Tygon tubing is used in a number of small fuel, oil-injection and bleed-line applications where flexible small-diameter tubing is required.

The transparent construction is particularly useful for service work because it allows the technician to visually inspect fluid inside the line.

Marine Bleed Hose Guide

Small bleed hoses are used within compatible engine fuel, lubrication, induction and crankcase-routing systems.

The required hose diameter is important because these lines connect to very small fittings and must fit correctly to prevent leakage.

Bleed Hose is Not Main Fuel Hose

Bleed hose should not be confused with the larger fuel-supply hose between the fuel tank and engine. Always use the hose construction and diameter specified for the particular engine circuit.

Marine Fuel Additives: What They Do and When to Use Them

"Fuel additive" is a broad category. Some products are primarily deposit cleaners, some are fuel stabilizers, some provide several fuel-treatment functions, and others are service chemicals designed for engine decarbonizing rather than routine addition to the fuel tank.

Choosing the correct product depends on what you are trying to accomplish.

Yamaha Ring Free PLUS

Yamaha Ring Free PLUS - 12 oz

Yamaha fuel additive formulated for deposit control and fuel-system corrosion protection. Yamaha states that it helps clean injectors, carburetors, intake valves, intake ports and combustion chambers.

Shop 12 oz Ring Free

Yamaha Ring Free PLUS - 32 oz

Larger-size option for customers who routinely treat fuel or service multiple engines.

Shop 32 oz Ring Free

Yamaha specifically recommends Ring Free PLUS for deposit control and protection of fuel-system metals, including protection related to the marine environment and ethanol-blended fuel.

Mercury / Quicksilver Quickleen

Quickleen Engine and Fuel System Cleaner - 12 oz

Quickleen is primarily a deposit and carbon cleaner. Mercury states that it cleans carburetors, injectors, intake valves, spark plugs, piston crowns and cylinder heads.

Quickleen is not a fuel stabilizer. If storage stability is the goal, use a product specifically intended to stabilize fuel.

Shop Quickleen

Sentry Fuel Treatment

Sentry Fuel Treatment - 8 oz

Compact Sentry gasoline fuel treatment for marine fuel-system maintenance. Sentry markets its gasoline treatments as multifunctional products intended to help with fuel stability, deposits, moisture-related problems and fuel-system lubrication.

Shop Sentry 8 oz

Sentry Fuel Treatment - 32 oz

Larger Sentry fuel-treatment size for frequent users, marine shops and larger fuel tanks.

Shop Sentry 32 oz

Follow the bottle label for the correct treatment ratio. Fuel additives can help manage fuel-system issues, but they are not a substitute for physically removing significant water contamination or replacing deteriorated components.

CRC Marine Gasoline Fuel Stabilizer

CRC Marine Fuel Stabilizer - 8 oz - 06161

Marine gasoline stabilizer formulated to help keep stored fuel fresh and reduce gum, resin and corrosion-related problems.

The 8 oz bottle treats up to approximately 40 gallons when used at the manufacturer's standard 1 oz per 5 gallons ratio.

Shop CRC 8 oz

CRC Marine Fuel Stabilizer - 1 Gallon - 06164

Bulk gallon size of CRC Marine Gasoline Fuel Stabilizer for marine shops, larger boats and customers treating larger quantities of fuel.

At the standard treatment ratio, one gallon treats approximately 640 gallons of gasoline.

Shop CRC Gallon

Johnson / Evinrude Engine Tuner

Johnson / Evinrude Engine Tuner - Gallon - 777189

Engine Tuner is different from a normal everyday fuel-treatment product. It is an engine-service cleaner used during tune-up / decarbonizing procedures to help remove gum, varnish and carbon deposits from rings, pistons, valves and ports.

Do not treat this as a routine pour-in-the-tank additive. Follow the Johnson/Evinrude service procedure and product-label instructions for the application being serviced.

Shop Engine Tuner

Which Fuel Treatment Should I Choose?

Marine Fuel Hose FAQ

What is the difference between Type A and Type B marine fuel hose?

Type A hose includes an additional USCG fire-resistance requirement. Type B does not have that Type A fire-test requirement.

What is the difference between A1 and A2?

A1 is the lower-permeation Class 1 version. A2 is Class 2. Type A1 is the normal Type A choice for fuel-feed applications.

Can I use Type B fuel hose below deck?

Do not make the decision based on location alone. Federal requirements vary by application. Type A1 is the straightforward choice for permanent fuel-feed applications requiring fire-resistant hose; Type B1 is only permitted in certain applications when the regulatory drainage conditions are satisfied.

Does hose inside diameter determine the clamp size?

No. Clamp size depends on the hose's outside diameter. Two hoses with the same inside diameter can use different clamps.

Can I use automotive fuel hose on a boat?

Use marine fuel hose that carries the certification and construction required for the application. Automotive hose should not automatically be substituted for USCG/EPA marine-rated fuel hose.

Can I use E15 gasoline in my boat?

No. E15 is not approved for use in boats under EPA rules.

Is ethanol-free gasoline always required?

Not necessarily. Many modern marine engines are designed to operate on gasoline containing up to the ethanol percentage specified by the engine manufacturer. Always follow the engine owner's manual.

Can a fuel additive remove water from my tank?

Fuel treatments can be formulated to address small amounts of moisture or reduce ethanol-related issues, but significant free water should be physically removed from the system. Do not rely on an additive to correct a badly water-contaminated tank.

Can fuel stabilizer restore old gasoline?

Stabilizer works best when added to fresh fuel before storage. It should not be considered a guaranteed method of restoring severely degraded or contaminated gasoline.

Is Ring Free the same thing as fuel stabilizer?

No. Yamaha Ring Free PLUS is primarily used for deposit control and corrosion protection. Fuel stabilization is a separate function.

Is Quickleen a fuel stabilizer?

No. Mercury identifies Quickleen as an engine and fuel-system cleaner. It does not contain fuel stabilizers.

How often should fuel hose be inspected?

Inspect fuel hose as part of regular engine and boat maintenance and whenever the surrounding fuel system is serviced. Older hose and hose exposed to ethanol-blended fuel deserves especially close inspection.

When should I replace a primer bulb?

Replace a primer bulb if it cracks, leaks, becomes extremely hard, remains collapsed, will not prime properly or shows other signs of deterioration.

Can Tygon hose replace my normal outboard fuel line?

Not automatically. Tygon is used for specific small fuel, oil-injection and bleed-line applications. Use USCG/EPA-rated fuel hose where the main marine fuel system requires it.

Are bleed hose and fuel hose interchangeable?

No. Bleed hose is intended for specific small engine circuits. Match the hose diameter, construction and application to the engine manufacturer's requirements.