Advice on Fueling Twin Outboards

[VeroWing]

I just removed a single 200hp outboard from my 22' boat, and replaced it with twin 115hp outboards. I've switched over all controls, steering, etc., now I need to deal with fueling twins. I have one line running from the tank to the fuel/water separator, with one line coming out. The I.D. of line coming out looks like 3/8"-5/16".

What I would like to do is, get a new fuel/water separator kit that has multiple outlets. Then I would run the one line from tank to new fuel/water separator, and then two lines out, one to each engine. Each line going to engines from fuel/water separator would have priming ball with one-way check-valve to prevent draining down one engine when other is running.

I've searched here and elsewhere, and still don't have solid info enough to determine if this is a secure way of doing this. I would imagine that a completely separate fuel line from the tank would be the optimum way to do this. I really don't want to start doing alterations to my below deck fuel tank if doing it the way stated above is a viable alternative, other than the fuel initially going through one line.

If anyone has any experience with this type of situation, I would really appreciate any and all information or opinions on the best way to proceed with this. Thanks, Mike.

 

[Silvertip]

Re: Advice on Fueling Twin Outboards

That's a reasonable approach -- provided the line and fittings between the tank and the WSF is large enough to feed the requirements of both engines. The lines between the WSF and the engines can be standard size.

 

[VeroWing]

Re: Advice on Fueling Twin Outboards

Thanks for the reply Silvertip. I was a little nervous about doing it this way, because I was told that this could blow a motor. I know that the engine I took off, 1989 Johnson 200, probably uses more fuel than the combination of the two I installed , Tohatsu 115s.
I'm going to check and see if I can increase size of initial fuel line and tank nipple, but I'm pretty sure from looking at it before(tank outlet) that it is welded in place on tank.

 

[ondarvr]

Re: Advice on Fueling Twin Outboards

A single large engine typically uses less fuel than two smaller ones, so you need to ensure the existing fuel line is large enough to supply both. If in doubt
replace it with two lines and two fuel water separators, this is a better setup for reliability, but either way will work.

 

[VeroWing]

Re: Advice on Fueling Twin Outboards

I wouldn't mind running two lines and separators at all. What worries me the most is getting another pickup installed into the fuel tank. It is an aluminum 96gal tank that is below deck, and is 3/4 full.
Does anyone know a source for pickup tube and fitting?

 

[ondarvr]

Re: Advice on Fueling Twin Outboards

You can tee off the current pickup fiitting at the tank.

 

[VeroWing]

Re: Advice on Fueling Twin Outboards

Wouldn't that be the same as splitting at the fuel/water separator?

 

[ondarvr]

Re: Advice on Fueling Twin Outboards

Almost, but resistance to flow (head) in a liquid is determined not only by the diameter of the hose, but by the length also. So in a short run you can get away with a smaller diameter than over a long run.
It would be nice to have two pickup tubes and it would be even better to have two separate fuel tanks, but you need to work with what you have.

If you need to buy another fuel water separator to get more than one outlet fitting, then the only difference in cost is the fuel line itself.

 

[VeroWing]

Re: Advice on Fueling Twin Outboards

Well, that sounds like a great idea. I think I'll do just what you said. I sure appreciate the ideas. Thanks, Mike.

 

[Silvertip]

Re: Advice on Fueling Twin Outboards

Installing a "Tee" off the existing bung in the tank does not solve the problem if the bung itself is too small. The smallest diameter in the fuel system between the bottom of the tank and the WSF is the constriction point in the system. With twin 115's, the system MUST be capable of flowing an absolute minimum of 25 gallons of fuel/hour because the two engines will burn roughly 23 gallons/hour at WOT.

 

[ondarvr]

Re: Advice on Fueling Twin Outboards

We don't know what size the current tube is, it may already be large enough to handle the flow. In a fuel, or any other type of system, there are frequently fittings and/or other parts that are a smaller diameter than the hose that carries the fluid, in fact all of the barbed fittings in the system have a smaller ID right now.

Whatever the system will flow now, will be increased with duel lines even if the pickup tube stays the same. The longer the run the, bigger the increase.

 

[VeroWing]

Re: Advice on Fueling Twin Outboards

I'll pull inspection hatch tomorrow and measure existing fuel outlet. Then I'll know exactly what I have. I'll post the measurement after I get it. Mike

 

[Silvertip]

Re: Advice on Fueling Twin Outboards

The fitting on the outlet of the tank is generally an anti-siphon valve. If installing new engines, I would at least replace that fitting with a standard hose barb. Then add two anti-siphon valves at the WSF. You will then know you've done what you can to reduce restriction to a minimum. I agree that the fuel pickup is probably sized to easily accommodate the two 115's. But as I mentioned, anything after that becomes a potential point of restriction that must be minimized.

 

[VeroWing]

Re: Advice on Fueling Twin Outboards

I received some great info from a fellow boater on my fuel feeding problem. He told me that many times the tank manufacturers will place two "tapped Bungs" on top of the tanks in case of dual feeds being needed, and place a plug in one. I checked my tank this morning and that is what I have.
I'll be able to get another pickup and run a completely separate line and fuel/water separater to each engine now.
I'm so happy that I won't have to cut and tap new holes in the fuel tank, and I won't have to worry about starving the engines.
Thanks for all the help and ideas. On to the next bump in the road. Mike