87 Dual Tank Issue

[jaxwithanx]

Hello,

I'm having a 383 built for my truck and in an effort to get more fuel was going to run a 155/L pump right after where my dual tank lines combined. Unfortunately, I have heard that somewhere in the return line (either the dual tank switch valve or the in-tank sending units) that flow will become restricted and pressure will build way too high and blow the line, if not more. Has anyone had any luck with the system I described above or ran into the problem I mentioned above? I have a 454 TBI unit ready to go and this fuel delivery issue is my last hurdle. If no one is positive about where the return line restriction is and how to fix it, anyone have any good ideas on how to get the fuel I need up into my engine (will need at least 18 psi and the stock pumps won't put out that even with a FPR). Here is the exact words of the guy helping me out on this -

Running a 3rd fuel pump will just add to the unreliable nature of the dual tank system. You need to change both intank pumps to the 155lph pumps. The issue with the dual tank trucks though is the switching valve under the truck. There are 2 pieces in the valves return line that restricts the flow as they were designed for the 1986 carbureted trucks and not for fuel injection which didn’t pose a problem with the wimpy 75lph TBI pumps that couldn’t pump more than 13-14psi anyway but these 155lph pumps can pump over 60psi of pressure and with that restriction that pressure will build to either the 60psi or blow a hose somewhere to relieve the pressure. Some 87 owners have reported that the restriction is in each fuel sending unit return at the top where the fuel goes back into the tank and others its inside that valve. They were used to prevent carbs from siphoning fuel back through the system. You can’t just blow through the line to find them either as air will pass through ok as well as “some” fuel just not enough when we double the fuel capacity. So check out those sending units really well when you change the pumps and if you don’t find anything there then rip that switching valve apart under the tank.

Thanks for any help. I know the majority of y'all don't deal with TBI systems unless you have an 87 or have converted. But I wanted to come to this sub-forum first.