Coughing (backfiring out the exhaust) is often (but not exclusively) a distributor that is too
far retarded. That would also account for the "low growl" you indicated you were hearing.
Turn the distributor counterclockwise just a bit, and see if she doesn't respond a bit better.
In the end (all other things being correct). You might want to keep advancing the dist,
followed by stabbing the throttle, until she "coughs" out the carb. Then back it up to
*just* before she coughs. That should give you as much "response" as the ignition
will provide.
HTH
--Chris
