FAT carb

I have a 850 Quickfuel carb. Its running extremely rich. I mean if its running in the garage for any time even with both doors open your eyes begin to burn. It has no adjusment with the mixture screws. Float levels are correct, secondary throttle plates are shut.
Could the power valve be blowin? And if so I have 5 inches of vacuum at idle, would I use like a 4.5 power valve?
Need a little input!