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