Stahl issues: Carb or Timing?

Try to get a vacuum gauge and tune your idle mixture to give highest vacuum, then turn the screws in (leaner) a 1/4-turn or so. You may have an overly rich idle that works when the engine is cold but gives too much fuel when warmed up. Also check to make sure your floats are set properly, if they're too high you can get fuel overflowing out the boosters and bogging your engine/stalling out when you hit the brakes or turn...