Ran my rebuilt motors today and got some misfires above 3500 rpm on port engine. Ran fine up to 3500. I noticed fuel pressure before leaving the dock was 3.5 psi on this motor compared to about 6 psi on the starboard at idle. Starboard started misfiring and was holding about 5 psi when I decided to ease back to the ramp. What psi should I be seeing from the stock 454 mag fuel pumps? Is this where my misfires like came from not enough pressure?

Your fuel pressure should be 6-8 lbs at any given time. The higher number should correspond to higher engine rpm.

From what you have describe, I think you are going lean on the one motor. Fix the pressure issue before you burn up a cylinder or two...

bad pump !!!!!!

every carb engine should only be 9 PSI max and 6.5 PSI min !!!!!!!

Thanks for input. My pressure would go down as engine rpm was increased. So I will change the mechanical pumps.

Does anyone know why the pumps lose pressure but no gas is seen in the sight hose for diaphragm rupture? Can you find an auto pump readily that matches up to the merc?

Use the merc pump...and get them from BAM marine.

I use BAM a good bit, just wanted to get back on the water this weekend if I could find an equal pump.

Try a local boating store..or place that sells/services boats ? Its Saturday, and they should be open. You may pay a little more, but at least you'd be out this weekend. I personally, would only run a marine pump.

Unfortunately the pumps at auto parts stores look similar, but will not work. If memory serves me correctly, the actuating arm on the pump is specific to Merc. Thats how they make their money. West Marine should have something that will work.

Yep, checked at my local merc dealer when he opened this morning and he didn't have a one in stock. So am out for the weekend. It may sound excessive but I'm buying spare parts to to have for this reason.

Not excessive at all sir.....it's called being PREPARED.

Alot more people should think like you.