86 C10 454 . Help with fuel return line. Pic's inside.

[Grit dog]

Mine is 86 non EFI. Im guessing the tank switch wont
take pressure being they were made for mechanical pumps

Afaik it’s the tank switching valve for carb or TBI trucks.
I’d say either something is plugged or you just have way too much volume.
Unless you’re making some serious power you have at least triple the volume you’d ever need with the blue pump. It’s orders of magnitude overkill. 30 gph pump doesn’t starve a Vortec 454 with a fuel sucking Edelbroke carb that gets 7mpg.
At idle, what’s it use? 2gph let’s say (maybe less)
Let’s say you’re returning “only” 100gph.
Quick math with 12’ of 5/16 return line, @100gph or 1.6gpm you’re returning about 800 TIMES the amount of fuel that line can hold, volumetrically, per minute.
That’s a lot of flow. And any minor losses (restrictions) will add up pretty quick.
Turn your garden hose on full bore open hose and the water maybe shoots out 2 or 3 feet. Restrict that opening and it shoots 20-30 feet. Same principle.
If you don’t find that it’s literally blocked and not returning fuel I believe this is the issue.

 

[Lowered87]

Holley makes a EFI retorfit for old school Chevy tanks. Edlebrock makes a fuel sump that goes under hood. Both kits are made to use the existing non-EFI fuel tanks.

 

[Nasty-LSX]

Talked to holley this morning. He said my fuel pump is bad because as soon as I connect the bypass return hose the pressure spikes up to like 20PSI when I only have a 14 PSI pump. WTF???? In my mind the regulator should
only let 6PSI to the feed(carb) and overflow goes back to tank.