Hard to believe that people (still) run a single plane manifold on a 454 or 502 marine engine (running less than 5500rpm). A good dual plane manifold will work much better than any single plane on almost any engine with less than 540 cubic inches. If you need more airflow, install a carb spacer between the carb and the dual plane manifold (850 cfm @ 5500 rpm is not enough?)! Use the out-of-the box jetting with a dual plane manifold and you will be jetted just fine almost every time.
Dennis Moore

Another question if ya don't mind.... what is your RPM at top speed with the 25P ?

Prop shaft center is the shaft that your prop is bolted onto. If your Bravo 1 drive is the same as mine (1995 Wellcraft Nova 23) and your cavatation plate is truely even with the bottom of your boat, then your prop shaft center is close to or exceeds 8 inches below the boat. So, your OD is creating allot of drag at higher speeds.

So your RPM is what, at your top speed of what??


edit;;; btw if that is THE Dennis Moore at post 21... listen to what he says.

'nuther edit... I just noiced you're running an elec fuel pump. I expect you have a regulator, do you have a fuel pressure gage?

THE Dennis Moore at post 21... listen to what he says.

+1 Get ahold of his book you will learn allot. Or give him a call, he has always been helpfull with me in the past. Visit his website