1957 18hp Johnson Seahorse fuel pump conversion

[Zachattack13]

I recently bought two 1957 18hp Johnson Seahorse motors and I only have a single line tank and I want to know what parts I need. I also need to know the spark plug type gap and fuel mixture if known. I'm also considering selling one, how much are they worth? Thanks in advance.

[samo_ott]

I was running my '57 J18 FD-11 today. A great 'lil engine. I run 33:1 in it but folks will tell you everything from 24:1 to 50:1. Plugs are usually the J6C or J4C and the gap is .030".

If you only got a single line tank, has it already been converted? Seems odd they would sell you two engines that require a pressure tank and give you a single line tank. Do both work? In my area a running FD-11 will get $300-$400 with tank.

To convert to a single line tank by adding a fuel pump, search this forum. There are many threads on it.

[Zachattack13]

The tank i have is from a newer engine, i found many threads but they are for much later years and i dont want to get stuck with the wrong pump.

[samo_ott]

If you PM me your email I will send you some info on it.

[tmcalavy]

There are several threads on converting similar year OMC twins to fuel pumps and even Mikuni fuel pumps...search for OMC fuel pump conversion. You need a single-line quick-connect fitting outside the cowl, a fuel pump, some fuel line, and maybe a fuel pump/bypass cover adapter. Should cost less than $75 or you are getting jacked on the parts.

[Zachattack13]

which pump will fit mine is what i need to know

[jdsgrog]

. I also need to know the spark plug type gap and fuel mixture

I have a '58 johnson 18hp fd-12. Spark plugs are j4c's gapped at .030 (j6c's work too, but the j4c's seem to run smoother). 24:1 fuel/oil ratio. these are based on service manuals.

Great motors, easy to work on.

[tmcalavy]

Don't know the exact part number for the stock OMC pump...maybe FR will chime in, he knows the numbers pretty good. If you search Fleabay for OMC fuel pumps, you'll get some hits/returns that list several pumps and have a cross-reference on the pump and years it fits.

which pump will fit mine is what i need to know

[TYRONE BROWN]

i recently bought two 1957 18hp johnson seahorse motors and i only have a single line tank and i want to know what parts i need. I also need to know the spark plug type gap and fuel mixture if known. I'm also considering selling one, how much are they worth? Thanks in advance.

thank you tyrone brown