I've posted about my remote tank solution for my Tohatsu 3.5 several times, but I finally got around to snapping some pics, so I wanted to show everone exactly what I'm talking about.
The impetus for this mod came after I pounded thru some wicked chop on long journeys, and was forced to refuel in less than ideal conditions. I've been tossed around on rolling 4 foot steep wind waves in about 25 knots of wind, and refueling in those conditions was messy and dangerous. I had thought long and hard about how to rectify this situation, including considering bypassing the internal tank to add an external tank. The problem with this option is that you need a fuel pump, which uses pressure from the cylinder head, and an associated hole popped in the head of the motor. No thank you!
My solution was fairly simple. Why not use a standard outboard remote tank fuel line with its priming bulb as a reserve tank, and pump thru the gas cap into the interanl tank? Well, it works great. Here is an image of the system:
In this picture you can see the remote tank, fuel line, modified gas cap, and standard gas cap.
I ordered the extra gas cap from a marine small-engine supply place. I found it by calling around till I found one that worked on tohatsu. This was the most expensive part at $20.
The gas cap on the tohatsu is plastic, and it has a plastic tipped "wing-nut" that screws down to cover a small pin hole vent. When I removed the wing-nut and drilled out the threads for the brass fitting, the pin hole vent was still there. I picked up a delerin washer that happens to fit perfectly over the top half of the fuel fitting, so it "hovers" about 1cm over the pin hole, allowing venting, but not letting any rain water,etc in. I'm not sure any rain water could really get in, but that is what I did. If the pin hole didn't exist on the Tohatsu cap, I would have simply drilled another hole in the refueling cap (note I kept my original cap because I need to put it back on to seal the motor for travel). Here is a close up picture of the cap, drilled for the fuel barb, with the fuel line clamped onto the barbs of the attatchment:
This next picture shows the inside of the drilled and tapped fuel cap. Note that I removed a rubber gasket that was clamped to the original wing-nut. The cap is probably less gas-tight, but I never leave it on when the motor is not installed, so it doens't matter. Note the brass fitting threaded thru the cap.
The tank vents perfectly well, however the little refueling bulb does take about 3-4 seconds to "re-fill" with fuel after each squeeze.
The brass fitting, the tank, and the refueling bulb all came from Boaters World, but they could come from anywhere that sells outboard stuff. The brass fitting is meant to screw into a a regular outboard extra tank, so it has threads on one side, and hose barbs on the other, with a "hex-nut" fitting in the middle.
The hose with proper fittings for the tank was about 15$, the fuel fitting $4, and the 3 gallon extra tank ~$10.
Putting the system to use requires simply screwing the cap/fuel line assembly to the motor when it is mounted, then attaching the fuel line to the remote tank down in the footwell of the cockpit. The fuel line snakes up over the tansome, and I tuck it behind the handle. Its long enough to allow the motor to rotate 180 degrees to allow for reverse.
From dead empty, the tank is full in 14 squeezes. I often simply top off the tank when entering a port, or occasionaly add one or two squeezes while motoring thru non-sailable conditions. I've even heard the motor "cough" a bit as it ran out of gas, and kept it running with a quick squeeze or two.