66;
If you're running the 2bbl Holley carb, did you change the power valve to a lower number, like 6.0 or 6.5 (stock is often 8 or 8.5)? Your vacuum, if you have the 2bbl, will tend to be lower at low engine speeds. This tends to let the power valve open too easily and lett too much fuel in, making it run rich. The result is smoke, both blue-white or black and sooty, and lots of that foul fuel smell, which is unburned fuel.
Changing the power valve to a lower number will tend to keep the valve shut until you accelerate (or hit a hill). Also, if you have any vacuum leak at all, the stock power valve will stay open at lowe engine speeds all the time, causing this same problem.
If you don't have a vauccum gauge, borrow one somewhere and do this:
at warmed-up idle, plug into a manifold port in the intake log with the gauge. Your engine speed should be 850 RPM or less. Your vacuum should be well over 12 In.HG on the gauge (more like 14-18 in. HG). If it is lower than this, there is a vacuum leak somewhere, like under the carb, and all of the problems mentioned above will occur.