Carb Help!!!

I made sure I had the 1/2 plug in the back,tried turning the idle screws all the way in and then out a turn and still the same thing. Since the 800 runs fine could it still be a vacuum leak or to much fuel PSI? Why would it run fine with the idle screw all the way in turning 2700 rpm's but then cut off if i back the screw out any ? It doesnt chug like its trying to die or struggle to stay running. Its literally an immediate cut off like fuel is cut to the carb. Im running 9 degrees BTDC aon the timing as well.