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