coachsmith wrote:Q1: what sort of two-tank fuel system can be used on a 170 MONTAUK boat?
Twin 6-gallon fuel tanks are often seen being used on small boats like a 170 MONTAUK. The general advantage of using 6-gallon fuel tanks is they can be carried to the boat. This permits the operator to remove a 6-gallon fuel tank from the boat, take the 6-gallon fuel tank by car to a highway fuel retailer, and then buy fuel at a highway retail fuel station, which is generally much less expensive than getting fuel at a marina fuel dock. This process, however, can be cumbrous, and lugging around 6-gallon fuel tanks full of gasoline is still a bit of a hefty load, and there is always a potential for some spilling or leaking.
The 6-gallon fuel tank was popular in the days of pre-mixing of fuel and oil in a 50:1 ratio. Six gallons is 6 x 128 = 768-ounces. Leaving room for the 16-ounces of oil means adding 752-ounces of fuel, so one-pint of oil (16-ounces) gave a ratio of 752/16 or 47:1. This made pre-mixing simpler.
Since you have made no mention of the type of engine you have, I don't know if you need to pre-mix oil into the fuel. If you do need to pre-mix, the 6-gallon tank may offer some convenience.
A general problem with a 6-gallon tank is you can never make use of all the fuel in the tank, so typically about a half-gallon remains when the tank can no longer deliver fuel. If another 16-ounces of oil is added and then the tank filled with fuel, this results in the oil ratio getting a bit richer each time. Eventually the oil becomes very rich in proportion to fuel, and the engine may begin to run rather roughly or make a lot of smoke.
The typical rigging for a 6-gallon twin-tank fuel system is to have a connector at each tank, and to have one fuel hose with a mating connector, primer bulb, and engine connector (assuming the engine has a detachable fuel connector). Some modern smaller engines in the 90 to 115-HP range may not have a detachable fuel hose connector.