I always use 20 Secs Carb down wind Ie BUMFICH (C for Carb)
Then as soon as you configure to start descent ie on base if flying cct then Carb on and power back to "descent setting" ie on PA28's approx 1500 RPM.
If you do a go arround must remember to put Carb Off. I have wondered on many occasions why I have sh
t performance in the climb. Oops Carb is still on. I have however found it don't blow up the engine as I was always told. I guess it don't do it much good though and the aircraft don't perform.
I must admit I never really saw the point of downwind carb as you put it on for a good long stint in the descent and final any way but old habits die hard and I ani't risking it now.