Another Carb/Timing Question, I am really not good at this stuff Options

[tornik550]

I have recently gotten my 914 up and running after a rebuild. I have been trying to work on the carbs and timing. The car runs ok but I am shooting black soot out of the exhaust and the exhaust backfires on decel. Engine idles fine. I have been reading and searching for a long time. I have read too much and I am now super confused. I keep reading that the backfiring on decel is from a lean condition and the black soot is from mixture being too rich? I am confused, can anybody help me? To confuse me more, I recently saw some white/blue smoke- I checked my compression and I am getting 150 in all cylinders.

car info
-73' 1.7 liter however I now have 96mm jugs, 78.5mm stroker crank- making engine displacement just under 2.4l.
-the previous owner put in a new camshaft however I do not know the details other than that it is from webcam
-2.0 heads
-cromoly pushrods with clearance set to 0 cold
-timing set at 27 degrees at 3000 rpm
-bosch 050 dizzy with pertronix
-msd 6al

carb info (all the jet/venturi/etc sizes were placed by the previous owner)
-dual weber 40 idf's
-carbs just rebuilt last week
-32 main venturi's
-120 main jets
-f7.5 emulsion tubes
-200 air correction jets

I am so confused.

Your help is greatly appreciated,
Steve