Mike,
I would check the cam with a dial indicator on all lobes, or replace it with a cam and lifter kit (because that what I would have done anyway). Then I would check the carb jets. If you have straight dual exhaust and are getting smoke out of both pipes, you are running rich on both banks. My guess is primary jets and/or power valve issue. Does your carb have the check ball to protect the power valve in event of a back-fire (Holley 125-500)?
This is standard on new carbs, not sure when it was introduced. A blown power valve will richen up the mix at all engine speeds
you may want to tune your power valve anyway (take idle vacuum and divide by two).
Found this bit of information on checking power valves
here A blown power valve will have the greatest effect at idle and low RPM. You can check the carb by unbolting it from the manifold, putting the nuts back on the studs, and plopping the carb onto the studs. If you have an electric pump, turn it on. For a mechanical pump, completely remove the coil wire, and crank for about 15-30 seconds. The manifold and carb will be separated by a 1/2 inch or so, enough to see if any gas drips into the plenum when the engine is off (Don't try to start it!). If gas is present, check where it is coming from. There is a hole near the throttle plate that leads to the PV chamber. A blown PV will cause gas to drip from this hole(s). If it is dripping from the bores, the float level may be too high, or your carb has a crack.Scott
