TR6 Engine Problem

[DuperSude@aol.com]

Hello all,
   Well our 71 TR6, A.J., is almost back on the road for the first time in 12
years.  We have one problem, though. Whenever we rev the motor and let off,
sometimes we expierence a pop back through the carbs.  We think it might be
the timing but we aren't sure.  The engine is a little lean, but we don't
think that would do this.  Any help would be greatly appreciated.
                       John & Danny Burket
71 TR6
76 TR6
69 GT6+
79 TR7 Coupe