Hi from Turkey,i have a stock 74 Firebird Formula 400..only got edelbrock performer series manifold and 500 cfm edelbrock carburetor..but i have a problem,when i step on the gas there is a black exhaust smoke.. why??everybody says that it should be carburetor not fit my spec. i should to buy 600 cfm..is it correct?if correct which brand i should choose ?rebuild q jet?600 edelbrock?or holley??