I have a 1990 Fleetwood Bro., 5.7L 357, dual exhaust flowmaster. When I crank it up black smoke comes out the exhuast pipes. I was told that my car was burning too much gas. When I hit the throttle it burst out a big puff of black smoke. What could be the problem? When i begin driving i have no problem with acceleration but when I let my feet off the gas petal it seems the car rpm just drops. If there is anyone out there with some helpful info please let me know.