i own a 89" nissan 240sx, it ran great when i sold it, but the girl i sold it to wrote me a bad check so i had to go get the car back, when i picked it back up it up it would not start, i changed the spark plug's and put in some starting fluid, and it started, i had it wide open and it would not rev up past 3k rpm's, but after driving it around the yard, now if i rev it up it will red line, so thats not the problem, but yesterday when i started it, it would barely run, and when i reved it up it sounds like a moaning dog now,lol, the timing is wright on it, and it did have some black smoke to, the car has some mods, it has been bored .30 over, racing cam, racing clutch, header, no catalytic converter and a magnaflow muffler, and a short throw shifter, so what would cause my car to run like this?