Q: hard start and hesition when warm on 1990 Pontiac Firebird

Rookie cbe0621eac06868b3efe0d8d1d3611e23c60d3114864ea2ec19a68cfbd3eebab
Let me start by saying my car is a 1968 pontaic firebird. When starting my car it starts and runs fine cold, when driven and parked for a short time it starts hard and hesits and sometimes dies at speeds.
I'v noticed alot of air bubbles in the fuel filter. I have checked and changed all the rubber fuel lines, also have changed the HEI Ing. Mud, but still doesn't seem to fix the problem.
I have done a complete tune up last year inculing the fuel filter. There is also a new carb on it(Holley 750).
(2) Answers
air bubbles are a proble. when the motor is hot, the fuel will boil without proper pressure causing your exact issue. have the lines air tested for leaks.

Sounds like vapor lock. This is more often occurring on modified vehicles, SInce you have a Holley 750, I assume you car isn't stock. Adding heat shields between fuel systems and hot components will probably help. There are also heat shields available for between the carb and intake in case excessive engine heat is boiling fuel in the float bowls. Check Summit or Jegs online for appropriate (and safe) materials.