My 327 CI (340 HP) 68 Chevy has a Saginaw 4 speed, and an 8 inch Ford rearend out of a 76 Maverick. The car is a steel bodied 23 Model T Ford Roadster that started out as a Roadster Pickup. The box was removed and a rear section from a Touring Sedan was added making it a big two passenger hot rod. I have 202 heads and Sanderson headers along with an Edelbrock 750 CFM carb and a K&N air filter. I just finished doing a tuneup on it and it seemed to run fine but has now started running rough and surging after the motor gets warm (around 180 degrees). What is the probable cause of the surging. I have not opened up the carb yet. Thanks in advance for any and all help.