I'm running the KE blue mech fuel pump on a warmed up 525sc. Boats inning really crappy today. Loading up.. stalling..

I have an electrical fuel pump gage on the dash and it was pegged over 10 psi. Anybody ever have an issue with these making too much pressure?

Yes, I have. Check the vent tube. I’ve seen guys boost reference the top of the diaphragm in blow through setups, maybe it’s clogged and built some pressure above the diaphragm? Slim chance but worth looking at

Haven’t run into any mech pump increasing psi, but others have. I’d do what was suggested above. If that doesn’t work, it is more likely the top section that has issue. The big spring on top of ghe diaphragm is what set’s fuel psi.

The bottom section of the pump has the one way valves the ‘in’ has and the ‘out.’ If these vslves have an issue, little or no fuel psi would be the outcome as fuel can reverse direction thru part of the stroke.

Mine was at 9psi on my new engines. I added a fuel pressure regulator and dropped it to 7psi and all was good.

was the top half new too ? Been a bunch of oe and aftmkt mechanical pumps with too high psi issues.

Water in the fuel will give you all of those symptoms and make your gauge read high. I Just went through everything you have described on new to me boat and it was a tank full of water to blame.