Gas tank vs portable in 4hp

[Ben in Beaufort]

I recently got a used 98 year 4hp that has a gas tank builtin and the connection for a portable tank. Which one does it use? and can it use both?
The hose runs from the tank to the sediment bowl bypassing the fuel pump, and the external tank connecting hose goes to the fuel pump and then to a nipple at the top of the carbourator. What to do and of course I have no operator's manual. Perplexed

 

[itstippy]

Re: Gas tank vs portable in 4hp

I've never had a Johnson/Evinrude (OMC) with both built-in fuel tank and external fuel tank coupler, but I do have a couple Eska's like that and I understand the marketing concept. You are supposed to be able to run one or the other or both. The fuel is regulated by the carburator float, and the float bowl does not care if it gets fuel from the gravity-feed built-in tank or the pump-feed external tank. You use the built-in tank if you're traveling light (like duck hunting) and don't want to mess with a 3 or 6 gallon external tank. You use the external tank if you're going to troll all day and want a lot of fuel available. They're trying to sell the same motor for both applications.

I'd close the petcock on the self-contained tank when running the external tank. I have no idea why, but I would. Maybe so if I burn up 6 gallons of gas I'll have some left in the little tank to get home with?

 

[JB]

Re: Gas tank vs portable in 4hp

I had a 60s JohnnyRude 3 with both. There was a valve to select which fuel source to use. it was between the fuel pump outlet and the carb. Look for that valve.

Failing that, I think if you turn off the outlet from the integral tank and hook up an external tank you will be able to use the external.

I had that 3 on a little 7' SportYak II. It ran an entire season on one 6 gallon tank and had some fuel left over.