I have a 1989 Nissan pick SE. VG301 motor V6 2WD with 127,000 miles on it. I recently had to change the heads due to a timing issue which froze the valves up and I lost compression. Since the new heads have been on I have got poor poor gas mileage and heavy black soot in tailpipe, so thick its eaten a hole in the pipe. As driving I feel like a backpressure or surge when gas pedal is not depressed. I was unsure of vaccum lines and where to re attach them. Any suggestions as to what is causes the poor gas mileage and can anyone provide me with a detailed diagram of the vaccum system. Mainly the lines that go to the throttle body or intake?