after building my motor,car starts but i cant drive the mazda.i put it on drive and the car shuts off. i took to my boy that has alot of years dealing with mazdas,and he just called me to tell me that he cant find the problem.he has changed carbs,checked the whole vacume system and still nothing.everything is stock and in working order. if anyone has had this problem ,please help me out. i drive it with the gas and brake together so it wont shut off.

sounds like a vacuum leak or something. trans doesnt have a lock up