I would try swapping the props at this point. I can not think of anything in a Bravo drive train that can "Slip" without metal shavings (internal or external) everywhere and failing soon after.
Just remember after you swap props, forward and reverse are backwards now. Maybe they are not matched, but it is a quick check.

Do both engines run the same r.p.m. at WOT?

I currently have 3 blade 23 pitch stainless mirage props on both drives and to my knowledge both drives have the same gear ratios. I have closely inspected both props and neither has cracks, chips or dings.

The port engine runs about 600 rpm higher than the starboard.

So do the motors eventually both turn 5000 rpm, 23's the 502's should push you to about 67 to 68 on the top end.


If they eventually even out maybe you are just cavitating the props, at what rpm do you push the throttles forward, out of the hole or do you wait till the boat planes off and the props are hooked up, 3 blades will cavitate out of the hole pretty good with that boat.

Throttle linkage check?????
You said the motors were removed for rebuild.
Maybe the linkages are not set correctly?
Carbs? Swap carbs and see if it follows?
Vacuum leaks?? Sucking to much air higher in rpms??

This will sound stupid, but check the plug wires (or broken plug). I got a boat back from the shop once and they had swapped the wires on the wrong plug. You would be surprised how good it runs like that, barely noticeable if your not ready for it. I chased all sorts of leads trying to figure that one out. Boat went 43, then 58 with the wires straightened out.

Just a thought.

I would guess this is obvious, but when you had the overhauls, did you remove the motors, or did your technician do the entire deal? If they did it, make this their problem. If you took out the motors and had them rebuilt, then reinstalled them yourself, I guess would think that the problem is somewhere on the motors if everything else ran fine before the rebuilds...leading me to believe this fix might be something rather simple...but you will need to knock them off one at a time to determine the problem.

I agree. It definitely sounds like the port side is not doing it's part of the work. Sounds like the starboard side is doing nearly all the work.
May be there is less slip initially when you get on plane, from the port side and then it starts slipping after you are on plane.
Otherwise I agree to let the port side do more work when getting on plane to verify that theory.

Are the hubs of the props with rubber insert or solid ? If they are with rubber I would suspect a prop problem.