How to Replace an Outboard Fuel Line and Primer Bulb

When to replace. Replace the line and bulb if you see any of these:

• Hose that is hard, cracked, swollen, sticky or soft and spongy
• A gas smell when you wipe the hose with a dry rag (the hose is breaking down)
• A primer bulb that won't firm up, is stiff and hard to squeeze, or is cracked or swollen
• Fuel weeping at a connector, or connectors that no longer click and lock
• You don't know how old the line is

BoatUS notes that fuel hose has a useful life of about 10 years and that older hoses may not be compatible with ethanol fuel. Yamaha says that if the bulb won't get firm and there is no leak, the bulb should be replaced. BoatUS adds that a stiff bulb usually means the small one-way valves inside are failing, and the old rubber can shed bits that block fuel flow. Don't try to soften an old bulb.

Know the hose ratings. The Coast Guard rules in 33 CFR 183.540 define four types of marine fuel hose, all based on the SAE J1527 standard:

• Type A hose also passes a fire test (it has to hold fuel in a fire for a set time). Type B does not.
• Type 1 hose has low fuel permeation (fuel vapor seeping through the wall). Type 2 has higher permeation.
• Each hose must be printed on the outside, at least every 12 inches, with "USCG TYPE A1" (or A2, B1, B2), the year it was made and the maker's name.

For a fuel supply line, BoatUS's advice is simple: buy A1 (or the newer low-permeation A1-15 when available). It is the most fire resistant and least permeable. Never use automotive fuel line, vacuum hose, clear vinyl tubing or garden hose.

The EPA rules too. On top of the Coast Guard hose types, EPA emission rules (40 CFR 1045.112) limit how much fuel vapor can seep through the fuel lines of outboards and portable marine tanks: for lines made from 2009 on, and for primer bulbs from 2011. EPA lets makers certify a portable-tank line as one assembly of hose, primer bulb and self-sealing connectors. That's one more reason a complete, labeled kit from a marine supplier is the easy choice over a line pieced together from random parts.

Know your connectors. Quick connectors are not universal. Mercury/Mariner (and some Force engines) use a clip-on style; Johnson, Evinrude and other OMC engines use their own clip-on style; Yamaha uses its own connector; Suzuki, Honda, Tohatsu and others may use their own or one shared with another brand. A Mercury product listing, for example, describes separate connectors for Mercury-style and OMC-style clip-on fittings, both for 5/16-inch inside-diameter hose. The simplest path is a complete fuel line kit labeled for your engine brand and your tank. Bring the old line to the store if you're unsure.

Match the hose size. Use the same inside diameter as the original. Many small and mid-size outboards use 5/16-inch hose and larger ones often use 3/8-inch (typical; confirm in your manual or on the old hose). The primer bulb and connector barbs must match that size.

• Installing the primer bulb backward, with the arrow pointing toward the tank.
• Using automotive, vacuum or clear vinyl hose instead of USCG-rated marine fuel hose.
• Buying a "universal" kit whose connectors don't fit the engine or tank. Owners of older engines often report aftermarket end fittings that look right but let air in (the bulb never firms up and you hear a gasp of air at the engine end with each squeeze); a genuine connector for your engine brand usually fixes it.
• Forgetting the small O-rings inside the tank and engine fittings. On an engine that sat for years they're often hard or cracked, and a new line can't seal against them.
• Skipping clamps on the bulb ends, or using cheap clamps with steel screws.
• Overtightening clamps with a power driver until they cut the hose.
• Leaving the line too long so it kinks under a seat or hatch.
• Pumping an old stiff bulb harder instead of replacing it.
• Starting the engine before checking every joint for leaks.

• Any fuel leak or gasoline smell inside the boat (stop and call; don't start the engine)
• The fuel hoses run under the deck or to a built-in tank you can't reach without removing panels
• You suspect the anti-siphon valve, fuel pickup or tank fitting inside a built-in tank
• The engine still starves for fuel after a new line, a clean filter and a clear tank vent
• A connector on the engine itself is cracked or leaking (the fitting on the cowl or bracket)

• Carry a spare primer bulb, two clamps and a short piece of A1 hose in your toolbox.
• Write the replacement date on the hose with a paint pen and log it in BoatMend; plan to replace it again in about 10 years, sooner if it shows wear.
• A fuel-demand valve between the tank and the bulb can stop pressure in a hot portable tank from pushing fuel through the engine. Ask your dealer if it suits your setup.
• Squeeze the bulb before every trip: it's the fastest fuel system check you can do.