Mercury 40 HP EFI Uses 1/4-inch ID Fuel Hose

A conversation among Whalers
DEBoater
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Joined: Sun Jul 25, 2021 11:16 am

Mercury 40 HP EFI Uses 1/4-inch ID Fuel Hose

Postby DEBoater » Sun Jul 25, 2021 11:20 am

My [unidentified Boston Whaler boat is rigged with a] Mercury 40 HP EFI outboard that has a 1/4-inch ID fuel hose under the [engine cowling]. That hose mates with a 1/4-inch to 3/8-inch adapter in the [stern] that is on a hose that runs to the [fuel] tank.

I do not understand why a 3/8-inch or 5/16-inch ID hose isn’t used inside the engine cowling.

I am [new] to boating but generally good with engine mechanics.

jimh
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Location: Michigan, Lower Peninsula
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Re: Mercury 40 HP EFI Uses 1/4-inch ID Fuel Hose

Postby jimh » Sun Jul 25, 2021 1:20 pm

What year and model is the Mercury engine you are asking about?

A modern 40-HP outboard engine at wide-open throttle will probably consume fuel at a rate of not more than 4-GPH.

Fuel hoses of 3/8-inch-ID are suitable for up to 300-HP which might consume 30-GPH. Rigging an engine with 40-HP with a large diameter fuel hose might be a bit excessive.

Also, on many modern outboard engines the hoses found under the engine cowling are often pre-formed hoses to fit a particular curved shape. Forming 1/4-inch fuel lines may be easier or cheaper or both.