manifold vaccum for vaccum advance ?'s

Ok update. I set the initial timing at 16 degrees wich lands the total at 34 degrees 18 degrees in the distributer. I set my vaccum advance can to give out 15 degrees of timing at 18 inches of vaccum. wich cruising own the highway in overdrive would be a total of about 48 to 50 degrees of timing.
I took it out for a drive and it was running good, but i didnt notice some smoke coming out of the exhaust when i backed off the throttle from getting on it pretty good? this never happened when i was hooked to manifold vaccum.... And another thing, i got home let it idle in the driveway with the vaccum advance hooked up to ported vaccum and it is still faintly popping out the exhaust... so what in the hell could be causing this? I am no longer running the vaccum advance off of full manifold vaccum and it is still thudding and popping out the exhaust sitting at 16 degrees initial wich is this motors sweet spot. This is frustrating me to no end.