Dual 392 engines can not share a single fuel pickup tube from gas tank

Yes they are

 

cool, I learn't to drive trucks in an international with a 392 and 13 speed roadranger. In the late 70's and early 80's there were thousands of them in australia, mostly cement trucks. I did not know there was a marine version, very robust old engines.

 

Palmer marinized thousands of International engines, link shows a label. They were driven from the front, so turned around, flywheel was free of the velvet drive transmission.
Port side engines spun in the reverse rotation. They also had manual adjusted valves, not hydraulic. And used a bypass oil filter, not a full flow filter. Those 2 things were not great ideas.
I added full flow oil filters to both my engines when I rebuilt them.


Feet 1969 Palmer International 265 HP Engine - 31324 | Antique Boat America http://www.antiqueboatamerica.com/Boat/_Feet_1969_Palmer_International_265_HP_Engine_31324

 

I think it is too much suction head to the most remote pump. You said that the main filters are reduced to 1/4", which is less than the 3/8" piping everywhere else. Area of a 1/4" pipe is 0.049 sq in, 3/8" pipe is 0.110 sq in, 1/2" pipe is 0.196 sq in. So the way you said you have it piped means that flow is totally restricted to ~half of what is needed to keep a single 3/8" line flowing. As Rumars said, full flow through a 3/8" line should keep a much larger engine feed, but you have reduced flow to less than a 1/4" line. I would re-pipe everything from the tanks to the main filters in 1/2", and from the filters to the pumps in 3/8" to prevent starving the pumps.

 

ALl the original fittings from 1970 are 1/4" NPT pipe connections, for valves, tanks, fuel selector manifold, etc..., with 3/8 hose barbs, an easy to find size.

The only real difference, is I am using electric pumps, not mechanical diaphragm which is what engines originally had.

I plan to do an open flow test with both pumps on and see if they keep up equally.

 

Quick note
In the picture of your fuel manifold, there appears to be a spring loaded fuel valve. I am pretty sure that this type does not meet ABYC regs I believe that they do not permit tapered fuel valves with a spring to load the surfaces
If the spring should corrode the mating seat pressure reduction would allow the valve to leak.
Not sure if the other valves are internally spring loaded

Also the two upper fittings should have the longer hose barb as the others appear to, to allow proper installation of TWO marine hose clamps, stainless with the screw/worm being stainless as well and not the
cheaper automotive style with the galvanized screw/worm

Not sure what you used as a thread lubricant but these need to be the type that will not be impacted by the fuel type. Ie teflon tape tape or similar product

These joints almost look soldered??

 

yes, all soldered together by me. Guaranteed no leaking ever. Reason I did that, yeas ago was having a problem with the suction side pump losing its prime, so eliminating any possible issues. That one turned out the brass metal dip tube in the tank had corroded to bits.

lead solder and brass go together very well, those valves will never leak ever. Plastic tapes are bad, they can break off into the lines, chemical sealants can fail. I took valves apart before sealing them with solder.

All the valves are spring loaded, most the spring is internal. These are cylinder cone valves, have not heard the ABYC no longer likes them, the springs are SS inside. These are likely 50 years old, good for another 50 years. They can get gummed up stuck, to free, you pop them up out of their cone seats, then they will move again, otherwise you ill strip or bend the handles
And I found the problem. The little fuelfilter in front of the Facet pump was almost blocked, totally clogged up. took out boat without the filter, and it worked without stalling for fuel.

It is supposed to be a screen 74 micron filter, and I had mistakenly put in a 10 micron filter. So I ordered the correct 74 micron Facet protect the pump only filter from Aircraft Spruce.

You dont really have to use this, I have a large 10 micron fuel separator before the pump, but this is it here as a guarantee the pump wont get stuck with a bit of this or that.
FACET FILTER FOR SOLID-STATE PUMPS | Aircraft Spruce https://www.aircraftspruce.com/catalog/eppages/facetpumps3.php

 

Brass Fuel F/F Shut-Off Valve – 1/4″ FNPT | http://www.moellermarine.com/moeller-marine/fuel-accessories/brass-fuel-ff-shut-off-valve-14-fnpt-033303-10/
WEST MARINE Shut-Off Valves | West Marine https://www.westmarine.com/buy/west-marine--shut-off-valves--P013854773?recordNum=4
Moeller 033300-10 Shut-Off Valve Ma/Fem 1/4\" Br | Seattle Marine https://www.seamar.com/item/MOE033300-10/SHUT-OFF-VALVE-MA-FEM-1-4-BR/

Says these meet ABYC? Same valves.

OK, yes ABYC rules allow spring loaded tapered valves if the spring is internal. External springs not allowed. look at 24.8.5
https://law.resource.org/pub/us/cfr/ibr/001/abyc.H-24.1993.pdf

easy enough to change that one valve if i wanted. I will tell you a 50 year old boat ABYC wont like anything about it.

 

24.11.8
Hose used in the fuel tank vent system or the fuel distribution and return line system shall be secured to a mating spud, pipe or fitting which is formed or machined to provide serrations (at least 0.15" [.38mm] depth) or a bead.. At least one corrosion resistant metallic clamp shall be used with a band width as indicated in Table III

Double clamping with 2 clamps only on the fuel fill, (24.11.7) not on the fuel distribution system according to ABYC which can be one clamp. See personal preferences and opinions are distorting the truth as written in the ABYC requirement. I see that all the time in life. People are very opinionated, especially when they claim to be an expert, but often their facts are just opinions and personal preference, even though they insist they are right and even if shown will argue with you forever that they have the best way to do things. Honestly dont even try to talk to them, you will keep the peace,otherwise get ready to argue and fight over a lie.

 

I had to look this up as well. I also erred in saying that you need 2 hose clamps on the fuel line, and/or return line if the hose is attached to a serrated hose barb. Evidently, you need two clamps on the fill pipe/tank and 2 clamps if you are slipping the hose over a smooth pipe, but ONLY ONE if the hose is on a serrated hose barb on the draw and or return line.

 

Well at least you admit it, many wont.