1980 after warm up idles rough and is tough to start after warmup

I have a 1980. Stock small block minus the catalytic converter system and some headers and true duals installed She starts great cold and after it switches to low idle is fine....until I have driven it for 3-4 miles. It then runs rough at idle. Today was a warmer day (70's) & after driving it for an hour I stopped at a store. When I came back to the car after 10 minutes it cranked over solid but didn't start for about 6 seconds...then stalled immediately. I then tried to start her again and had to give it several pumps of the gas pedal to get it started....about 10 seconds to start it. It ran pretty rough at stop lights. At first I thought the low idle just needed adjusting and maybe new spark plugs and wires as the heat may be affecting them. Now I am wondering if it could be something else. Anyone have a similar experience.....suggestions and opinions are appreciated.

|UPDATED|4/20/2016 12:53:24 AM (AZT)|/UPDATED|

first look for a vacuum leak to carb or it could be time for a carb rebuild

 Sometimes when an engine runs OK cold and then has a problem when it warms up, it's due to the carburetor leaning out once the choke ceases forcing a rich condition.

Ok..so check carb for fit and mixture......

I would agree with @73shark and look at your carb. Sounds like a Q-jet in which case I would go ahead and rebuild it and when reinstalling I would look at all vacuum lines and make sure I had no leaks. I installed an Autometer Vacuum gauge under the hood that comes off the intake manifold so I can always see how many inches of vacuum I am pulling and makes adjusting timing and carb settings much easier.