I have a stock remanufactured 1978 305sbc. I added a Holley 600cfm (vac. sec.), a Edelbrock Performer intake and a set of Hooker Headers. The timing was set at 14 BTDC with a total advance of 44 BTDC using stock HEI. The vehicle was getting 12.5MPG consistently.
In the attemt to increase mileasge and performance, I swapped in a Holley 390cfm and a new HEI distributor with a 50000 volt coil and new wires and plugs, of course.
After adjusting everything and running the vehicle for a few weeks, the mileage has actually "DROPPED" to 10.7MPG.
OK-now-shoot!!! Tell me whats wrong!!