Rear spark plug appears rich

I've been trying to adjust the carb after installing the cv performance upgrade kit, e-zjust screw and such. I've been checking the plugs and have noticed that the rear plug is usually rich looking. What would be causing the rear cylinder to be richer?
With the kit I originally installed the 46 idle, 185 main. I wasn't able to get any adjustment out of the mixture screw, so I installed the 45 and 180. Still seemed to run good, but no adjustment out of the mixture screw. I have no tach so I think I'm going in circles here.

set the idle with the throttle stop at a little off idle lets say 1000 rpm after its warmed up turn the idle mixture screw all the way in and wait about 5 seconds the motor will seem to run a little rough start to back it out slooooow and when you hear the exhaust sound crispy your set . take it off high idle and set it to your liking not to low . its has to have some rpm in it to have oil pressure . and we aint got but 5-6 pounds at idle around 900 .!!! rpm.