At 1-1/2 to 4 lbs. fuel pressure, You are literally running out of fuel!
You are about to start learning fuel systems first hand.
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Fuel pressure for a Holley should be taken from a line as close to the float bowl as possible. No Holley fuel feed line should be under 3/8" for any reason.
Fuel pressure for a Holley should be in the area of 6 to 7 PSI on a Gauge (PSIG).
If you are still using a mechanical fuel pump, it's going to be difficult to feed any high performance carb, mostly because of the lines that feed the pump.
(Usually around 5/16" ID for stock lines)
You can try one of the high volume mechanical pumps, but I haven't had much luck feeding the beast with them... The stock lines are usually to restrictive.
Generally, even if you go to Holley 'blue' pump and regulator to increase volume, you are still limited by the crappy little 5/16" or so lines that are factory stock.
I'm sure if you have a vacuum secondary carb, the stock Holley transfer tube to the back float bowl isn't feeding the back Venturi during hard passes.
One thing I would look into is the needle and seat. Some holley needle and seat arrangements used in the smaller carbs are too small to feed the beast. That problem shouldn't turn up as low fuel pressure though, it should turn up as lean plugs after a hard pass.
You need to start by finding out what line you have coming from the gas tank. If you have a 3/8" or larger INSIDE DIAMETER (3/8"ID) fuel line, and you inspect it from tank to fuel pump for damage, (bends that kink, bends tighter than 3" radius, mashed flat spots (anything that reduces the diameter of the line by 1/4 or more must be replaced),
3/8" fuel line should do the job you want to do with a stock engine.
--Or you can get new 1/2" ALUMINUM line for your fuel line. Aluminum doesn't really cost that much more, sheds heat a lot better, and is much easier to work with.
Remove the original mechanical fuel pump, fuel pump rod, and get a block off plate for the hole in the block. Run the new line right up the front of the block to somewhere you can mount a regulator.
Don't use any 90 degree fittings if you can help it. Every 90 deg. fitting reduces fuel flow by approximately 5 to 10%, depending on line size.
(changing the line gives you the opportunity to shield it from damage while 4 wheeling)
Install a Holley 'Blue' electric fuel pump as close to the gas tank as you can.
Install a Holley fuel pressure regulator as close to the carb as you practically can.
Use as little rubber line hooking things up as is possible. Rubber line on the suction side of the pump WILL get sucked flat, and become a restriction if allowed to.
Don't forget to get a fitting that will allow you to install a fuel pressure gauge, and install it AFTER the regulator.
Install as large of fuel filters as you can get away with.
Use a metal case one before the pump if you can, and use just before the carb also.
(a bunch of people will argue, but as the gas tank degrades with age, and as the gas quality gets worse here, a filter in front of the pump will keep that crud out of your expensive pump & regulator. A second filter, after the regulator, will keep any debris from a bad fuel system out of your carb, and insure a clean fuel supply.)
Mount a gauge OUTSIDE of the vehicle passenger compartment (in case the fuel line to the gauge breaks, you don't have gas inside the vehicle), where it can be seen by the driver.
If you still loose fuel pressure now when you launch, you may need to put a 'sump' in the back of the tank. The fuel may be climbing the back wall of the fuel tank, and uncovering the pick up tube for the pump.
See if you still loose fuel pressure now.
So many cats, so few recipes...
