Fuel Problems? Help a brother out

[Dsutton5107]

New on here,
I tried the search but didn’t find exactly what I was after, maybe I just missed it. Anyways figured I post and look for the help this way.
I’ve got an ‘81 Chevy K30 3+3 Silverado package. Truck came factory with 350 SM465 NP205, previous owner put a sb400 in it. Engine was pretty tired though by the time I got it.
Doing a restomod build. I’ve done a lot but having troubles with the last little bit. I did a 454/NV4500 swap. NP205 was swapped for a rebuilt 205. New drivelines, exhaust, cooling system, interior, Dakota Digital gauges, bench seats from a 2010 Silverado. Engine was build but an outfit that makes high HP and racing motors. Engine was on Dyno running at 560 hp.
Now to the problem I’m having. So I replaced the fuel line from RH tank all the way to the Carb. I’ve replaced the Fuel Selector Valve and Switch, Mechanical Pump (Holly 454-13), Hanger. New carb that was on with Dyno (Holly Brawler double pump 850). Basically all new fuel system on RH. But it is not getting fuel correctly. I did the old Gatorade bottle test and wasn’t pumping any fuel at all while turning it over. So next I put the new fuel line into a independent gas can and the truck started and ran on its own for 5+ minutes before I turned it off. After hooking it back up, still nothing. It wants to start but just won’t or might start for a few seconds and die. My initial thought was bad fuel pump so I sent it back and got another with the same problem.
Any suggestions on where to go from here?

 

[6872xtc]

Awesome truck!

I would look into a possible leak in the lines causing the pump to suck air for the first step. The pump could be bad of course, new stuff isn't guaranteed to work 100% . But there is a decent distance for the pump to pull fuel in a long truck like that, so anything that isn't perfect can cause an issue.

Oh, and try to verify that the selector valve is working properly and isn't pulling a little air from the opposite side. Maybe it's partially shifted?

 

[imiceman44]

/\ /\ this

You must have a leak or possibly the valve is switched halfway or the wrong side.
I mean it's obvious the pump works if another tank bypassing the fuel lines is working

 

[Blazooki]

All new hoses back at the tank right?..No chance there's a piece of old hose that's soft and getting pinched shut when the vacuum starts?

 

[Dsutton5107]

All new hoses back at the tank right?..No chance there's a piece of old hose that's soft and getting pinched shut when the vacuum starts?

No all new hoses.

 

[Dsutton5107]

So update, I’m no farther than I was before. If anything I’m back two steps.

I went to run the same test again (gas line in gas can) and it wouldn’t start. Battery was dead, finally got it to start and I had a real strange noise, almost a humming sound then died.

I was going to replicate the test in front of the tank selector valve and then again behind the valve to determine whether the problem is there or behind it from the tank.

I’m just at a real loss here.

 

[Wes Harden]

I had a brand new Ac Delco 40gph mechanical pump, my truck would run idle well 1st and 2nd gear ok, but 3rd and 4th at highway speeds would starve. I put a 38GPH electric at tank and it runs great. Your motor probably needs more volume than my 355 qjet set up

 

[6872xtc]

Did you confirm that there was gas in the carburetor? If it is full, then the accelerator pump will have a nice shot when you crack the throttle. But I would try this with the engine off and looking down the carburetor.

 

[Justin V]

If it runs on a different tank, check for kinks in the line to the real tank. Try blowing air through the lines or something.