3.3HP Mercury Outboard, convert to remote external tank possible??

Todd RT

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Joined
Mar 28, 2009
Messages
18
I have a 2001 Mercury 3.3hp on my dinghy. Would like to convert it to an external remote tank.

After looking thru schematics of various Merc outboards, it looks possible, but isn't the internal gas tank gravity fed vs a fuel pump??

Any suggestions? Or is this impossible?
 

emckelvy

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Jan 16, 2004
Messages
2,506
Re: 3.3HP Mercury Outboard, convert to remote external tank possible??

Todd, all you need to convert any gravity-fed outboard to a fuel pump system is a pump, fuel lines, and appropriate quick-disconnect fittings for the motor and remote tank.

The fuel pump requires a source of crankcase pressure/vacuum in order to "pulse" the pump diaphragm and provide pumping action.

Typically this is done by either attaching the pump directly to an intake port cover (with a hole in the cover going directly to a port in the fuel pump) or, via a fitting in the crankcase which connects via a vacuum line to the remotely-mounted fuel pump.

In your case you'd be looking for a fuel pump that uses the 2nd method, and has a 'stand-alone' fitting to connect via hose to the crankcase.

The challenge is gonna be from where to get your crankcase pressure/vacuum source. If you have any kind of tapped hole that's now plugged and leads directly to the crankcase, you can install a fitting there and connect to a fuel pump.

This has to be in an area that's past the reed valves and before the intake ports, i.e., sees both crankcase pressure and vacuum.

If you don't find a readily-available hole, you could drill/tap one. But you're on your own there, I couldn't recommend doing so without diassembling the block to see where such a hole would work. If you don't take it apart, you drill at your own risk. Just be sure to use a vacuum cleaner to keep the chips out of the innards!

The rest is a piece of cake! Just find any old fuel pump that'll physically fit in your motor, fab up a mounting bracket and hook it all up. I've done this to quite a few motors and it sure is nice to have a remote tank.

Be sure to pick up a 'small engine' in-line fuel filter and place it between the pump and carb. This'll take the place of any filter screen which may have been in the gravity-feed fuel tank.

BTW, the pump don't care what motor it's pumping for, so don't just look for Mercury stuff. Any brand'll do.

HTH........ed
 

Todd RT

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Joined
Mar 28, 2009
Messages
18
Re: 3.3HP Mercury Outboard, convert to remote external tank possible??

Wow, thanks Ed. appreciate the details for sure! Sounds over my head with the vacuum coming from the block. If it was just the rest, sounds doable.
 
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