1958 Johnson Seahorse 18 FD-12

[nathankukson]

I have been trying to get my recently aquired 1958 Johnson 18hp motor running.
This is a list of what i've done so far:
Cleaned Carb
New Carb Kit
New Fuel Filter
Replaced all Ignition Components:
Points(set at .02), Coils, Condensers, Spark Plug Wires, Spank Plugs
New Impeller
Cleaned inside of gas tank
New Gas tank Gasket

When I got to starting it it starts right up and idles well for a good 30 seconds and then dies. It seems as if it is not getting enough gas. I can keep it running by pressing the fuel pump on the tank. My best guess is an air leak somewhere along the way, but the gas tank is properly sealed so i'm kinda stuck. It's a double line pressure tank.
Any suggestions?

 

[1946Zephyr]

Re: 1958 Johnson Seahorse 18 FD-12

is the cap on tight when you start it up? After it dies, loosen the cap and see if a lot of air comes out. If not, then the motor isn't charging up the tank. That would usually mean that there is a problem with the check valve that feeds air to the tank.

 

[lindy46]

Re: 1958 Johnson Seahorse 18 FD-12

Also, try raising the gas tank. It's been my experience that on some of the pressure tank motors, if the gas tank is too low (much lower than the motor), gas won't get to the motor properly.

 

[nathankukson]

Re: 1958 Johnson Seahorse 18 FD-12

I tried it again today with the same results. I raised the tank off my floor and that did not seem to help. After the motor died I removed the gas cap and no air came out so the tank is not being pressurized. So like you said i may have a problem with the check valve or the air is leaking somewhere along the way. How can I test to see if the check valve is working properly and if it is not is it easy to replace and repair?

 

[lindy46]

Re: 1958 Johnson Seahorse 18 FD-12

Can you blow air into the air side of the hose going into the tank? If not there is a clog that needs to be cleaned out. You may need a complete rebuild kit for the tank mechanism, not just the gasket. Pretty simple to rebuild.

 

[levi_tsk]

Re: 1958 Johnson Seahorse 18 FD-12

is it possible someone converted it to a single line system and removed the check valves?
mines like that but i did it and i saved the check valves my personal opinion is that you should put a fuel pump on it but thats just me .....

 

[boobie]

Re: 1958 Johnson Seahorse 18 FD-12

I'll go along with the fuel pump idea, that way you will eliminate all the pressureized tank probs.

 

[1946Zephyr]

Re: 1958 Johnson Seahorse 18 FD-12

is it possible someone converted it to a single line system and removed the check valves?
mines like that but i did it and i saved the check valves my personal opinion is that you should put a fuel pump on it but thats just me .....

All 18's 1960 and newer had fuel pumps, so you can make an easy conversion.

 

[samo_ott]

Re: 1958 Johnson Seahorse 18 FD-12

I'd fix the tank. Shouldn't be that hard. Figure out why it's not holding air pressure. Gasket on the cap? Hose leak? There's not much to it. That's one of my favorite engines.