Just installed 2 mercruiser gen 4 fuel pumps. Started the engine and the holley carb overflowed with fuel. I tried to adjust the floats..no luck. I installed fuel pressure gauges and I couldn't believe the pressure at idle..12 psi and at 1300 rpms it pinned the gauge to over 15..wow. I have never seen such high pressure from a stock pump.
Has anyone ever seen this. I never had regulators before

Update... I called Mercury Marine today and told them about the 12 psi at idle.. They said that's alot of pressure but did not say it was a defective pump. He said some run high and it will calm down after it breaks in. They offered me a thicker gasket to put between the pump and the block to change the amount of travel from the plunger riding on the cam. I didn't like that idea so I decided to do the regulators instead.
Is there anyone else who had stock merc pumps with high pressure?

It is a known issue. For a while we would not sell the OEM pump. If you try and push on the pump arm you will see the spring is really stout. That is what determines the pressure.

It looks like the newest batch have been fixed.

I installed pressure regulators..I'll know tomorrow..hopefully it will work

make sure the tygon hose is not clogged it will cause the same 12-13 lb psi check the vent tube hope it hepls.

What is a tygon hose ...the vent tube is dry..no leakage

tygon is the material the vent hose is made of .its connected to the fuel pump if plugged it wont pump seen it many times . coast guard always checks for that hose to be in place .must be the brite yellow color

it makes more pressure than it was designed to. that means it makes more pressure than it was designed to stand up to. i would replace it/them.

Oh ok..Now I understand..That hose was changed years ago..but not with the brite yellow..These pumps are brand new from mercruiser model # 862049A1. Superceded from 814624A2. Mounted on block 1990-1992
465, 502 mag, 600sc. No regulator ever needed until now. Hopefully the regulator will keep the pressure at 6.5 without bouncing around. Changing the pumps and sending them back to the dealer is a royal pain in the A_ _..

same thing with my new fuel pumps. Had 11psi at idle so we put on regulators. my engine builder said this was pretty normal. Mine are sea pump mounted