I have posted hear before with great success and I need your guy's help again. I have a 383ci motor with a 350TH. I just took off my 850cfm Holley and put on a 600 cfm edelbrock so I can rebuild the 850. Well the problem is consistent with both carbs. After letting the car warm up to operating temp. and drive it for about 20 minutes, the car stalls, stumbles, and then starts to backfrire, and then it eventually just turns off. This chaos all happens within about 20 seconds. Also the car will not start unless it has been sitting almost all day, or until it completely cools down. It sounds really bad when I try to turn the engine over after it dies. I have MSD ignition, mallory 140 fuel pump, unilite dist. It has been happening for a while now, not consistent with any temperature of the car or the weather. I have always guessed it to be related to vapor lock or something along those lines. Could it be that the fuel is boiling before it gets to the carb. Any tips would greatly be appreciated.