I've got an 4150 that was older, but new. I put a full holley kit in it, just to make sure the gaskets were perfect. It's dumping fuel out the boosters. Not a drip, but a steading gush. I've changed needle and seat 3 times, no luck. It's just the secondary. I even changed the bowl, just to make sure it wasn't a float problem. It's a 440 with a stock replacement carter pump, not a high pressure unit. Fuel does not come out the vent. Any ideas?

sounds like a float problem.

Never had one do it in the secondaries but in the primaries it was a blown power valve...Now I just block them-off...

It's weird. No power valve, and I've ruled out the float by changing the bowl. If it were a pressure issue, I'd think the front would be leaking as well.

is fuel running out at float level check hole with plug removed?

throw it in the trash and replace it with an Edelbrock 750m

You seem pretty sure it's not the float. There is a plug instead of the rear power valve, right? Wrong gaskets maybe? Can you swap the rear metering block to the front and see if the problem moves?

If the float has a hole in it and is sunk, nothing you do will fix it short of replacing the float with a good one.

I rebuilt a 750 Vac sec recently that had sat for a number of years, float sunk and it spewed fuel everywhere. Replaced the float, runs great.

Well, I ended up changing the rear bowl and metering block, same problem. I hooked up a pressure gauge, only to find 11 psi out of the stock carter pump. This is the stock replacement style pump. I've never seen one that high.

It's the m4845, which is a muscle car replacement for 70-71 cars, rated at 5.5 psi, or so they say.

From what I understand the spring stiffness (plus the passage dia's) controls the psi and the lobe reloads (compresses the spring) so I'm wondering if an assembly line guy accidently (or on purpose ) put the wrong spring in there as it was going down the line

I've had problems with that fuel pump in the past, mine pumped out 10+ psi & blew past the needle/seats, get you a different pump.

if your needle isn't seating properly you can have this problem.
i know with my carb the jet extenders can cause interference with the floats also.

I just switched to a new carter M4589, stock style pump, and the pressure is 6 psi. All is well.