I can give that a try. Yesterday I repeated the test on the hose with the drives off and the port was still lower rpm by around 200 at any given throttle position. Even at right off idle which acts like throttle cable. But when you dry check throttle positions the blades are always dead even. Very interesting. I then swapped and reinstalled the drives and retested. Port still down. I then swapped carbs for the heck of it again. Still port down. Rechecked vacuum with these engines. Both identical. At idle (about 1050 rpm) both have 10". At 2100 both have 16". Both engines exactly the same which doesn't scream hurt engine to me..... Again. I keep gravitating back to the boat! On a good note the alignment job was perfect. The drives come on and off like butter now. What am I missing on the boat that could cause this lag with or without load?? Voltage drop, ground issue, interference?? There is no misfiring at all I can notice and both engines fire on the dime. Almost instant. I am going to do another compression check and write down psi for every cylinder and post it up later. But like I said based on what I'm seeing and the history of the boat I am not quick to point finger at hurt engine. Not yet. Does this make any sense or have I officially gone wacko?

Something else I have not swapped are the headers. They are stelling dry tails. I can't see it but could a header problem cause a 500 rpm loss in a 750 plus HP engine? Seem like a lot of power drop but is that possible?

didn't read the whole thread,,but have you checked that all cylinders are hot when running.sounds like 1-2 cylinders aren't firing.

Yes all cylinders firing. The issue appears to be the same issue as the previous engines had. Same exact loss of rpm on the same side. Both these new engines dyno'd within 1% of each other

Can't remember if you said if you tried swapping fuel lines, other than an electrical issue how the problem could remain after rebuild.

On next water test I can bring a 5 gallon can and pull fuel out of that to the mech pump. But it's not acting like its starving in fuel at all. Never hesitates, lean pops, or dies. Plugs all match the starboard motor in fact. It'll go WOT no problem from a stab. Just down on power anywhere and everywhere from idle to WOT. I also have o2 bungs I may just snag a wideband reading. Doubt it's fuel but something to rule out.

There was a thread a few months ago about filter seperator housings and different port sizes, a shot in the dark but who knows.

Thanks I will run on a standalone fuel cell next run and report back

post # 62 for starters run the engine that is down on rpms with a 6 gallon portable fuel supplu and new fuel line and primer bulb. Just for starters to see what happens to rule out if its a fuel delivery problem on the boat side. Just saying

Assuming the distributors were run in the engines on the dyno, and you are using MSD boxes, unplug or remove the rev limiter. If possible swap the boxes unless they were used on the dyno. We're the fuel pumps used on the dyno, if not you should check actual pressure running.