Mercruiser 3.0 stalls when accelerating

Boat wasnt running until I rebuilt the carb. Now that it turns on and can idle just fine and even get into first gear in the water I am now facing the problem of the boat stalling when I try accelerating past first. Advice please to why this is happening and what I can do to try to fix thank you.

I had a similar problem with my 5.7... idled fine, ran fine if I fiddled with the throttle as I shifted into gear and once I got it running over about 1100 RPM. After much fiddling around, I discovered that when I first moved the throttle, there was a very slight, barely perceptible delay in the movement of the accelerator pump linkage. I had just rebuilt the carb (ethanol junk problems). What I finally noticed, was that MERC had painted the carb after it was assembled and installed on the engine. This paint formed a zero clearance bearing on the connection points of the accelerator link rod ( that Z shaped wire rod that goes from the throttle arm up to the accelerator pump arm). One you dismantle this connection, which you need to do to get the top off the carb, the paint gets chipped off and the link connections to the throttle arm and accelerator arm get "sloppy". This allows the throttle plate to start to open BEFORE the accelerator pump squirts gas into the carb throat. The fix, recommended by one of the pros on this forum, was to VERY slightly straighten out the bend in the accelerator link rod so as to take out the slop in the linkage. A very slight CAREFUL straightening out (i.e., make this rod longer) with two pairs of pliers, is all that's needed.

Since this engine wasn't running before, you should also check that the advance springs aren't rusted and the advance mechanism in the distributor moves freely. Remove the distributor cap ( do not disturb wires to plugs) and see if you can turn the rotor slightly, i.e., about 10 to 15 degrees and that it snaps back when you release it.
If it does not move freely, you may be able to clean/fix it if you are handy enough... BTW... there is no "first" in a boat. All boats have fixed reduction transmissions and don't "change" gears ( other than Forward/neutral /reverse).

I'm not much of a boat mechanic as you can see and only starting looking into theses things after the problem came up

i was thinking its a fuel delivery problem because under a load she is not getting the fuel needed...I'm thinking it might be a weak or bad fuel pump but I want to make sure it is before paying 140 for a new one...the fuel was changed and we tried checking the antisiphon valve but it is so damn tight we can't get it off the fuel tank so we are going to bypass it by using another gas tank

And to add to that when I took the fuel pump out and checked it, the area above the diaphragm was filled with some sort of rusty powder either from the rusty filter that was in the pump some time back or from the actual spring connected to the diaphragm