Cavitating is like you're driving a manual transmission car and the clutch is worn out, the engine speeds without "hooking" with the water.
I'm not sure if you had your carbs off but I'm wondering if maybe the throttle cable is too lose and not opening the butterfies to full open? In case this is what's happening, I'll explain how I adjust the throttle cable:
First, loosen the two jamb nuts on the cable sheath at the carburetor and back them off to their respective end of threads to create space for tensioning the cable.
Place throttle control lever at full throttle stop (balls to the wall) position at the helm, and climb back into bilge.
Pull cable sheath tight while holding carburetor bell-crank to full throttle position and spin jam nuts against the sheath bracket finger-tight then use 10mm open-end wrench to lock them.
Place helm throttle to idle position and check the carb idle stop lever is resting on the idle speed adjustment screw. At this point there should be a slight only, almost imperceptible amount of slack in the inner wire of the throttle cable.
If the cable adjustment is too lose the carb butterflies might not open 90 degrees to air flow thus your engine speed will be limited.
Maybe that's the issue (misadjusted throttle cable)?
Okay, the other possibility of limited engine speed happens if the RAVE valves (ie:787 & 951 motors) aren't opening, they will build carbon on them and stick so they must be removed and cleaned periodically (~ once or maybe twice per season). Once disassembled, I use a solvent or oven cleaner to clean the carbon deposits and sticky oil varnish from the RAVE blades so they move freely in the RAVE slots.
