I could use a little help with my carburated Evo engine. The rear plug is black with lots of soot. Its a new plug. The front plug looks fine. Fuel mileage is poor at best. Im running a Crane Fireball Hi-4E in in single stage. The carb is a stock CV from around 1993. It was probably re-jetted in the past but, Im not sure. I have the mixture screw set to 2 1/2 turns out from bottom. Idle at about 800. I just resealed the intake and repaired a broken vacuum line so I dont think there are any vacuum leaks. I am not using the VOES. i have the vacuum line plugged off going to it. Seems like the Crane is making the necessary timing adjustments OK. So, what could be causing the rear cylinder to run so rich? Thanks

 

Try new wires, you may not be getting a good enough spark and it wouldn't hurt.