Dual Tank Plumbing Question from Jet Boat Noob

[twowheels]

I've been boating for about 10 years, and after starting with a Yamaha LS2000 twin jet boat, have had a couple I/O boats in between.

Just picked up a tricked out (ie mutilated) 73 Rally Sport Hombre turned hot-rod.

On our 1st time out yesterday, it ran OK at first, then started dying at about 2krpm, and finally would not stay running. We limped back by waiting a minute, after which it would start and run for about 30 seconds. repeated 8-10 times, then pushed with oars and boat hook lol.

Initially i thought it was a midrange jet problem on the Holley double-pumper, but then when it died altogether i suspect fuel starvation.

After I thought about it last night. here is m working theory:

The boat has twin tanks, one on each side. They appear to be plumbed with just a T fitting before the mechanical fuel pump on the olds 455. I filled one tank but not the other before going out. Awesomely cool dual fuel gauges don't seem to work.

So I'm now thinking the other tank was near empty, and when it got below the pickup it started sucking air, resulting in no draw from the other tank. I there EVER a case where a T fitting works with dual tanks? Doesn't make sense to me.

There are many things on this boat that make me think it was set up but never run. The place diverter trim cylinder disconnected from the arm on the short ride. The throttle pedal was set up with about 1" of travel 0-WOT (which I noticed and fixed before our 1st run)

Also, the fuel tank vents (or are they returns) are capped, which seems wrong as well. I understand in a boat these are normally vented to atmosphere.

I'm thinking no matter what, I should replace the T fitting with a selector valve. doing a little web research it seems I should go with a 3/8 valve. Will probably go mechanical. I haven't found a cheap enough electric one (want marine, not automotive), but open to options if someone has a suggestion other than the GM truck one.

[XstreamVking]

Tanks have got to vent... Might have been the problem. Pop the fill caps to allow vent for testing. Selector is good to have, but the tee will drain both tanks and feed ok. They will equalize fuel levels thru the tee.

[CharlieN]

Nothing wrong with a Tee, it needs to be down low and they are best used with low outlets on the tanks. The vents do need to be open and possibly tee together but not necessary.
With a selector valve you can easily suck one side low pretty quickly, but gives you a good reserve. Some boats are sensitive to the imbalanced fuel load, some are not.

[leaky]

The problem with a T is you pretty much never draw the same from both tanks - so sooner or later you are going to run out of fuel on one tank and run into what you have experienced...

The best of both worlds would probably be to put a shut off on both tanks before the T. Then you have the options of running on both or 1 (or get a valve that goes 1/2/both).

What you are finding that's capped could be the vent or a 2nd vent or intended for a return, a second pickup, etc.. etc.. But for sure you need a vent, so if you can see the whole tank and have no vent then time to add one. FYI - IMHO it's good to add a shut off valve to the tank vent (nothing fancy, a home depot valve is fine), basically so in the event the boat is going to sink you can at least close the fuel system off.

Jon