That "aluminum plate" is a metering block.
I really don't care for those too terribly much, but I have used them with success. If it ran before (but the Percy Plate), I would say it could be two things. You say it ran for thirty minutes, did it run good? or ran limited and was a turn from the start?
It sounds like there is a systemic issue with the fuel system. Does it lose fuel pressure at anytime? Do you smell fuel when it poops? you just cant get it to start?
Do you have a spare ignition coil? It almost sounds like the coil is taking a dookey. They will run until it overheats and shorts out, when they fail, they can do what you describe (run like absolute crappola).
Go to Greg, plead your case, but be cool, just explain the situation. It does not sound like he rebuilt the carburetor and also sounds to me like he was apprehensive about the repair. I personally would ask for an hour of troubleshooting so he gets an opportunity to save face and if he finds a failed coil, bad fuel pump, or something else, it will be on you, if you don't feel warm and fuzzy before the work is performed, take your boat and thank him for the hour. He may not go for it, but at least it will be a civil agreement.
When I had my shop, I would get boats that were hacked all to hell from other shops and shade tree mechanics and I can't tell you how difficult it is to catch "everything" on a once-over. I had a slight advantage because we had access to a water dyno, we could ring the hell out of them a few pulls to get an idea what it would do on the lake.
Unfortunately it meant pulling the engine and mounting it up, a three hour minimum charge. But it could save a lot of frustration. Add to that, my shop was less than ten minutes from a lake...
Good luck...
GT
