I'm running one ( mechanical sec. annular booster 750 ) on my 408. Verdict is still out, as I only have about 10 passes on it. The 4 corner idle circuit seems extremely touchy. I'm only out about 1/2 turn on the mixture screws. More than that and it goes rich. Center air bleed is wide open. Other than that, it seem to work ok. I made multiple changes when I changed carbs ( reads stupid ), so I don't have a good carb comparison.