My 64 122, B18 w/ dual SU's, idles rough. The motor was tuned up (new plugs, points, cap&rotor, timing set, etc.), the motor is smooth and stong when revved (81K miles), but below about 2000 rpm the engine gets rough, it rocks like it has a misfire to it. I pulled the wires one by one and noticed that the 2 rear plugs (the 2 cylinders closest to the firewall), when disconnected, don't seem to make any difference in the idle. That leads me to believe the problem is with the rear carburetor and further evidence is the black sooty plugs and when lifting the piston of that rear SU the engine speed doesn't change much, but when I do the same thing to the front SU, the motor gets rough. Both of the SU's were disassembled and cleaned by the previous owner and the linkage, throttle shafts, choke adjustment, etc. all look fine. Both have hydrolic fluid in the caps (looks like clean motor oil) and I tried adjusting the jet mixture, but no matter where I adjust the jet on the rear carb, up or down, it doesn't change the idle. I'm thinking maybe the float is misadjusted, dumping too much fuel at idle? Any other ideas?