<VV> Greenbrier stumble

[Gary]

OK, my 63 Brier has a 110 car motor in it. When cold it runs great, after it
has warmed up the motor "breaks up" on acceleration, occasional backfire. Of
course it idles perfectly.
So far: New Coil, condenser and points. Plugs,cap and wires are 2 years old.
Played with the timing, and carb adjustment.
Also recently adjusted the valves using the cold method and it runs better
than ever but still the hot stumble. It did do this before adjusting the
valves as well.
It goes down the road OK at a steady pace, but not under acceleration.

What am I missing.......

Gary Swiatowy