My bro removed the carb from out 82 ski nautique and had a guy rebuild it for us, using the rebuild kit from discount inboard marine. The guy has built many engines and carbs so i assumed he knew what he was doing. Well he must have missed something, because now the boat will crank and run perfect above 12-1500 rpm, but WILL NOT IDLE for anything If you try to let it run below 1200 RPM it dies. What i think they call the "booster venturis" seem to be dumping fuel down on top of the butterflies. I took the float bowls off and the float height appears to be right or very close according to some info I got off of the holley website. this is a marine carb and does not have the sight holes in the top of the float bowls, so no cheating and adjusting the float height externally with the engine running. ahaha just kidding. but it is kindov a pain.

We've moved the idle adjust screws every which way but all the way out and it doesn't matter. (of course, because there is so much raw fuel just being dumped in it.
So what could the guy that built the carb done/missed that would cause this.
The choke is operating properly and we checked everything we could find for vacuum leaks.

We also took the carb off of my brothers supra (exact same holly 4160 , but is not the marine version and it does have the sight holes in the top of the float bowls.) and the boat cranked, idled, and ran great. There was of course no raw gas visible from the top being dumped down into the carb from the "booster venturis" (if I'm calling the right thing?)

any ideas or anything i'm not an expert buy any means but this has me baffled. any help is greatly appreciated.
i dont know what is wrong i'm in noo way a carb guru or anything, the engine ran decent before, it would idle great and rev pretty good, just when it was in the water and under a load it would pull right.
we put a points elimination kit in the dizzy and were really hoping that from that and redoing the carb we would be ready to go with this thing. so i'm pretty disappointed right now. anyways, any advice or recommendations are greatly appreciated.

 

Remove the needle and seat assembly and see if there may be a small piece of debris in there.

 

Was the power valve replaced in the rebuild? Is there back fire protection on the Holley? IF not even a slight backfire can blow the power valve. But check as said the needle & seat first. I have had trouble with the Holley 4175 doing something similar & I set the floats a tad low to stop the fuel dumping.

 

If you turn the idle screws in till they seat (be careful to just feel them stop and don't force them)and the engine hasn't died the power valve is most likely supplying fuel thru it's vacuum passage.