Fuel pressure drops off idle
 

I have a carbed 454 MAG mildly modified with Holley 800 and Merlin single plane manifold, GIL exhaust and KE High volume fuel pump and MSD igniion.

The fuel pump is mounted on the sea water (GEN ?) pump. The fuel pump and carb are new; all new fuel lines. The engine starts right up and idles fine and I can pump rev the engine to 3000 and it sounds great. But if I try to sustain anything above about 1100 rpm the fuel pressure drops to about 1psi and the engine eventually runs out of gas. To make a VERY long (and expensive) story shorter, here is a summary of what I have done to trouble shoot: replaced the sea water pump; replace the KE fuel pump with a stock merc fuel pump; by-passed the fuel water seperator and fuel tank by connecting KE fuel pump directly to a hose into a 5 gallon fuel can. Checked all hoses; removed the carb bowl sight plugs and can watch the fuel level drop until the engine eventually "runs out of gas". If I pump rev the engine up to say 3000, the pressure jumps to say 7psi then drops. There is very little if any "smoke" during reving the engine.The thing will not hold fuel pressure above about 1000rpm. At idle pressure is 3-4psi. Is there anything in the carb that would cause such behavior? I have eliminated (i.e. replaced) just about everything else. Thanks.

Sounds like there may be a restriction in your fuel line plumbing. I'm assumming you are measuring fuel psi right next to the carb.

Seeing your other post about the seapump. Maybe the lobe in the seapump is bad or the belt is slipping.

Well, my local mechanic told me my seawater lobe was bad, so that is why I replaced it. Now I have a wobbling pulley plus low fuel pressure. I don’t think it is a restriction since I bypassed all hoses, separator, and tank and the problem remains. It seems like either a real coincidence: bad lobe and bad regulator on brand new KE high volume pump, or something wrong with brand new Holley 800. But I don't think it is the carb since it runs well, does not blow smoke and it takes about 1 minute to drain the bowls when the pressure drops. I may try hooking up test electric pump to see if it holds pressure to further isolate the problem.

The carb won't cause low fuel pressure, so eliminate that as an issue. You have a Gen V engine.
You did make sure the lube in the new seapump was full, didn't you???

Pressure should be 6-7 and fairly steady at all rpms. Your idle pressure is even low. Are you running a fuel psi regulator???

The problem can only be a few things.
1. Bad fuel pump or bad arm
2. Bad lobe in sea pump
3. Restriction in fuel line plumbing
4. Belt slipping
5. Fuel PSI regulator bad or not adjusted properly--if you're running one.

Good stuff
 

Griff-
Seawater pump is new so I don't think it is the lobe and yes I did fill the crankcase (to the sight plug) with the correct merc lube. The orginal DID have fuel in the crankscase and the lobe was bad. I did check and the belt does not slip. I did remove and check the braided hoses on pressure side of the pump. I made a "special" hose and connected from a 5 gallon can of fuel to the input side of the fuel pump, by passing the tank and F/W seperator.

The fuel pump is new, but I cracked open a new merc pump and installed a new Keith Eickert high volume base. The only regulator would be in the KE base.
I did use a new stock merc pump to test against and still had the problem, but this was on the orginal seawater pump which I beleive did have a bad lobe. If I eliminate the carb, about the only think left is the regulator in the KE base. My fuel pressure gauage is mounted right where the braided cable attaches to the hardwall fuel line to the carb. Thnks for your good advice.

Try the stock merc pump on the new sea pump. My best guess is the fuel pump is bad.
The stock merc pump flows plenty for your engine combo.