I just fired up my new 440 and it ran like crap. When I first fired it up I had fuel coming out both carb vents . I adjusted the floats what felt like all the way down ( turned nut clockwise ) before it stopped pumping fuel out of the vents ( Mechanical pump ).I haven't had a chance to pull the float level plugs to check the level with the motor running yet. The motor runs really rough like it has a couple dead cylinders but the exhaust temps ( taken at the header flanges ) are fairly consistent about 325 - 400 F. It idles just OK but when I rev it it has that dead cylinder shake to it. It did pop through the carb when I first tried to start it the dist was 180 out. I screwed the mixture screws all the way in and the motor died so I think the power valve is ok. The carb is a Holley 4780-5. The motor is new and everything on it is new or rebuilt. Is this a carb problem or could it be something else?

Motor info:
452 peanut plug heads
9.7:1 compression
Hughes whiplash muscle car cam
Performer rpm intake
MSD-6 AL
Stock dist
Blaster coil
Holley 4780-5 Carb. This carb was rebuilt by a meathead that put the metering blocks on backwards