was Carburetor gurus...

I am by no means a mechanic so maybe the terms might be wrong but this is the jist:

Question in regards to carburetors...my old 1986 PCM 351 Ford Winsor motor had an edlebrock carb on it...was giving me major issues, so we replaced it with a marine Holley 4160(I think that model)...and having trouble tuning it...basically it was pouring gas into the intake and making the boat flood and studder and die...we noticed a couple o-rings and thought jets and needles might be set wrong...so went for a carb rebuild...worked fine in the shop that night...no gas pouring in...came back to it in the morning to finish the spring tuneup and adjust and run compression...but started pouring gas again...back to the flooding problem...wondering if anyone has any ideas or even suggestions on what to look for? I have it at a marine mechanic and he has had it apart 3+times...just doesn't make sense...

Ideas??? Could it have to do with the fuel pump (mechanical one) putting too much pressure?

Thanks for any help...Nick