Backfire!

I'm looking for some advice from you gearheads out there.  i had the timing adjusted on my 68 Tri-Power because it was pinging.  Well, that problem was fixed but now I'm getting a slight backfire on a cold start.  Hot starts are no problem.  Any ideas what could be the cause?

Also check the choke adjustmets.

okay, after two weeks, i finally have some answers.  The timing is set at the officially correct setting of 4 degrees.  A good mechanic I know has recommended the choke settings be checked, just like Kyster here.  So we're going to do that.