I don't know anything about the Demon carbs,But 850 seems big to me, you sure that thing ain't dumpin so much fuel when ya hammmer it that it puts the fire out ???
seen lotsa guy's have the same type of problem with too biga carb on the street.
example when I ran big block circle cars
The shop that did the Alky Holley specified
650...... Those big carbs are fine for drag racin where ya never drop the rpms.....
But ya need to check what the other guys said as they are all good suggestions..