I have a Holley 750 double pumper with 30 & 50

OThe size of the Accelerator pumps is irrelevant. Jet sizes, air bleed info, and powervalve setup is what would give us more info. The list number off the airhorn would be good too.

Carbs
 

This is a link to my carb
http://www.holley.com/0-80528-1.asp

Nice. BUT WHAT SIZE JETS ARE IN THEM

How do I find that out?

If the jets have never been changed by somebody that does it regularly you will have to remove the fuel bowls and look at the numbers on the jets. They are stamped into the brass. Be mindful that you will probably need gaskets if they havent been off in a while. If you have had Jim or another mechanic ever do carb work they sometimes write the jet and powervalve size on top of the bowl.

Good luck!

Fixx
 

you need to do a run with the boat to determine if the jets need to be changed which they probably do before you pound the intake valves out of the heads..keep in mind that you can only go x amount of jet sizes before you have to raise the cfm on the carburetor so the engine will achieve the correct air to fuel ratio..

From the way it sounds you may want to have a experienced tuner tune them before you grenade the engines.

The jets are 73 front and back and power valve is 6.5.

Im gonna say that is no where near enough fuel/jetting for what you have. Especially if there is only a power valve on the primary side, and not the secondary side.

If it were me, i'd put 82's in the primaries, and 92's in the secondaries, and keep the 6.5 power valve, then go for a run and do plug checks. You may end up wanting a 4.5 pv with that large cam. But get some bigger jets in that thing.

Fixx
 

if you have bees running your boat like this i would als recheck your valve adjustment..pay close attension to the intakes..if thehe tip of the valve stems are higher then the exhaust you might want to look at intake valves..