az1966

car runs good and solid,,,, when down shifting or slowing down I get a slight pop'ing from the tail pipe.... 200 6 poper, 3 spd manual tranny,, no AC,, alittle ahead on timingby approx 3 degress,, new distrib cap and rotor, carb fuel / air mix at 1 1/3/4 turns any loer and the motor idles roughwhen warmed up

Daze

That is extra fuel burning in the exhaust. Basically when you shift down the RPMs suddenly drop but the fuel for the higher RPMs is still in the intake and the extra fuel travels out with the exhaust and ignites in the pipe. Sounds to me like the CFM of the carb is just slightly to big for the size of the motor.