I have a 1995 chevrolet C2500 full size truck. It has the 7.4 liter engine and was originally throttle body injected. It is now mutli-port injected with a system made by Edelbrock. It is running so rich it shouldn't be running. It blows black smoke on initial start-up, during moderate acceleration, and the occassional puff during steady state running. It idles poorly when fully warmed up. It is a well maintained work/personal vehicle. Until march of this year it was averaging approximately 10 mpg. From march to may fuel mileage slid from 10 to approximatly 7.5 mpg. it now resides somewhere around 6.5 mpg or so. The best part, there are no codes in the computer. The problem appears to be getting worse. Any guidance you can give would be greatly appreciated.