Fuel supply issues
 

Ok, I installed a new motor in my boat and I have been fighting what I believe to be fuel supply issues. It is a carb hp500 style motor that dynod at 684hp at 6200. It just seemed to lay down and had no top end, pulled plugs and they looked real lean. I went thru the fuel system starting with the vents, found both vents upside down and corrected, found orange crystals in one pickup screen, I eliminated both of those along with the anti-siphon valves. Drilled out and retapped separator orifices and increased the line size to 8an to the fuel pump. Replaced the fuel pump with a holley performance pump with 8an fittings, my pressure at idle is 8psi, I have not been able to verify the load pressure after the pump replacement. Compression is 165 across the board.

I pulled the bowls off the carb, fronts are 80s rears are 90s, bleeds are 28s and 70s. All the jets are clean. I did find the upper arm from the accelerator pump was hitting my throttle linkage bracket.

Do those jets sound reasonable? I am trying to find out if this was the carb the motor was dynod with. This thing is driving me crazy, any help appreciated.

What size carb is it?

What size pump? I'm having similar issues with the Holley red electric pump which only let's the 502/502hp motor rev out to 4800 regardless of prop.

Mechanical 170gph pump. Proform 1050 body with holley bowls/blocks.

I have ran a 26, 28, and 30 prop and no top end with any of them

I don't know these carbs well, but 80 jets sound very low.

Not the exact rule, but just an observance, :
Most 600's have 60 something jets
700's have 70 something jets
800's have 80 something jets
Most Dom's have high 80;s to high 90's. Some over 100.

That outa do it. Those jets do seem small.

Those jets sound very reasonable for that engine. I had a 900hp race engine in the past that had jets mid 80's and 90's with 1400 cfm pro systems dominator. The #1 thing you need to find out is fuel pressure under load to eliminate that possibility.

Well, after reading the hp500 carb issue thread, it sounds as though your jetting may be too lean. Apparently there is a major difference in marine carburetors that I wasn't aware of. Interesting.

check you metering block gaskets if its been apart and look for dirt in the bottom of the emulsion tubes too.

also check the float level this is number one cause if its low this will cause alot of problems make sure your using the 110 needle and seats or bigger if they make them remember thi and the regulator oriface are the smallest holes in the system and the limiting(restrciting ) factor