I have a 67 2bbs 289 I warmed up about 5 years ago. I have a petronix contact-less ignition and a HiPo distributor with a mild cam and 8:1 pistons with 83 5.0 heads and an endelbrock carb. car was running rich since I took it out this year and I swapped plugs and cleaned the carb. car ran fine but now pops back through the carb at any advance. under load it at times clearly misses. Any ideas as to what else I can look at?

 

Could be your accelerator pump is sticking. Try removing the plunger and cleaning it.

For future reference, I think you'll get a better response if you go to the VintageMustangForum (VMF).

 

Did you rebuild the carb or just clean it, could be a rebuild or a new one is in order