View Full Version : Advise for rigging new fuel lines on twin saddle tanks.

03-16-2010, 08:48 PM
Does anyone happen to have a fuel line diagram or chart for rigging twin saddle tanks? I made up a manual valve setup so I can isolate each tank with individual ball valves and only one gas line coming out, but I belive I am also going to have to figure in a return line from the fuel pump back into the mix. This is for my 1975 Starbuck Jet boat with a 402 Big Block and 12JC jet pump. It currently has dual 12 gallon saddle tanks, but the tanks use an electric selector valve operated by a switch on the dash that selects each tank. There is only one gauge on the dash for both fuel levels, and when you flip the switch it shows the fuel level for each tank. I want to eliminate the electric fuel selector valve and replace it with the manual system I made, so I can shut off both tanks, or shut one tank off at a time. I also want to retain the switch in the dash for the sending units for each tank, so I can check each fuel level. Any help would be appreciated. I currently have my 402 big block out of the boat, so now is the time to swap out the fuel system and I am getting ready to dive in there.


Mike in Missouri - pronouned misery :D

03-28-2010, 08:21 PM
Best way is to return bypass fuel to the tank, but it requires an expensive valve to do so. Some guys run it back into the supply, and can possibly cause cavitation. One way to minimize cavitation, is to re-introduce the fuel further away from the pump, such as into a dual inlet filter seperator.

04-14-2010, 02:20 AM
Thanks for the reply. I just fixed some older fiberglass delamination in my engine compartment, and had a new carpet put into the boat. Next is to use some Hurculine brush on bed liner inside the engine compartment to seal an protect my engine compartment area. Once this is finished, I am going to drop the rebuilt motor back in. I bought a new Holley mechanical marine fuel pump, it has an inlet and outlet and a vent line which I will hook back up to my existing vent hose going back to the starboard fuel tank. I am going to hold off on replacing the existing electric fuel selector valve for now, and swap it out later after getting the fresh rebuilt motor running again and get it broken in. I was really hoping someone that knew what was going on could sketch out a schematic for the dual tank fuel lines for a manual ball valve set up for me, but guess I will just go with what is already there for now. The only reason I wanted to swap the electric selector out, was the fact that it seems the starboard tank will overfill if I don't use it first. Somehow the port tank seems to vent over to the starboard tank. It's a goofy setup and I don't understand it, but will just not fill the right tank full and keep my eye on the fuel gauges more closely in the future. I do appreciate your response, I see many people have looked at my thread and you were the only response I received so far....have a good one!

Mike in Missouri. - Prounced Misery

04-14-2010, 10:14 PM
I ran a v-drive with twin saddle tanks. I finally settled on the following set up. It worked very well for me.
I installed a Holley electric pump on each tank with it's own switch on the dash. The fuel lines were plumbed to a tee and the tee fed the carburetor thru a single gas line. To avoid pumping gas from one tank to the other, I installed a one-way valve on each fuel line after the Holley pump. I picked up the valve at a diesel truck parts store. They were not very expensive and come in various flow rates.
This set up allowed me to draw from either tank by using the appropriate electric pump OR I could run both together which I did when at full boogie.
Having two fuel pumps is also a safety factor so if a pump fails, the other one should get you home.

04-20-2010, 03:42 AM
Thanks for your reply sir, I appreciate it.

Here is the setup I am currently using, that the boat actually came with when I bought it:

I have one fuel gauge at the dash board for both my fuel tanks. When I flip a switch on the dash, it manually selects either the port or starboard tank sending unit's. This dash switch is wired into a Pollack fuel selector valve and both the sending units are also wired to the Pollack valve then on to each sending unit. (This is similar to a chevy truck fuel selector valve for dual tanks) The switch controls an electrically operated pollack fuel selector valve that both fuel tanks are attached to, and the gauge reads the fuel level for the tank selected by the switch on the dash. There is only one fuel line coming out of the pollack fuel selector valve that comes forward to the inlet of my mechanical Holley marine fuel pump on the engine. My mechanical fuel pump has an inlet (from the pollack fuel selector valve line), and an outlet to the fuel supply line to the Holley 750 Double pumper carb, and it also has a vent tube on the top of the fuel pump diaphram that will connect back directly to my starboard fuel tank.

I have two fuel lines on the starboard fuel tank, only one fuel line on the port fuel tank.

One fuel line on the starbord tank is the fuel supply line that connects to the pollack valve, and one is strictly a return line from the fuel pump.
I am going to put in a fuel/water separator onto the line coming from the pollack selector valve before it is connected to my new fuel pump since the boat has never had one before. I was originally going to take out the electrically operated pollack valve, and replace this with a manual fuel selector assembly I made from all brass fittings. This has 2 manual ball valves, one for each side fuel line for each of the tanks and only has one exit line in the middle that would go to the manual fuel pump on the engine (looks like a T) with ball valves on each side. Since my starboard fuel tank already has a return line from the fuel pump, I decided to use this setup again. Most mechanical fuel pumps for big block chevy engines don't have a vent line from what I see online for seaching on big block chevy fuel pumps, and I originally was wondering if I could just eliminate that line back to the starboard tank and plug it off at the tank or not.
Since this is gasoline, and our lives depend on this working correctly, I didn't want to chance messing around with this, unless somebody actually knew what I should do for sure. I decided the Holley marine mechanical fuel pump (attached to the motor) was the way to go, because this is what type of fuel pump was there originally (mechanical). I didn't want to use regular fuel hose from the pump to the carb, so I went with the new Holley Marine mechanical pump because the fitting connection holes in the pump were compatible with AN style fitting threads (NPT) threads.
I am running Russell 3/8" Stainless Steel braided lines with 6 AN fittings from the pump, to the new Jegs 6 AN fitting style fuel filter, another 6 AN Russell Steel Braided line runs from the other side of the fuel filter to the carb line. I bolted on a new Stainless Steel braided line setup on the carb (two steel braided lines into one fitting) so the russell fuel line with 6 AN fittings would bolt up to it. I also purchased a Jegs fuel pressure gauge to go into the fuel line on the carb supply line, there is a spot I where I can attach it. This way I will know how much pressure the line is under with motor running at idle and at wide open throttle. The new Holley Mechanical Marine Fuel pump, stated I did not need to have a fuel pressure regulator in the line for this pump, so I am omitting one.

Hopefully it will work fine once I drop the fresh motor back in. I still need to get a fuel/water separator with a spin on type filter to put in the main fuel line to the pump. I don't really want to run the engine without one. I could end up sucking up some crap or some water from my fuel tanks and ruining my new fuel pump or carb if I don't put one in.

Hopefully someday I can eliminate that fuel return line back to the starboard tank, and just have a single line coming from each tank to one line to the fuel pump with a T valve assembly that I made, so I can manually shut off each tank separately. Of course this means I would have to wire up the fuel tank sending units to bypass a pollack valve that will no longer exist, since this is where all the sending unit wiring is currently attached. Hopefully I can figure out what is right, and safe and just do it myself. Nobody in the state of Missouri will work on a Jet boat...just because it is a jet boat...pretty strange if you ask me but that's okay who needs them...except maybe for some advise.