Carbon deposits on only one plug

[DEAN911]

'73 MFI with a new motor kicked up to 2.7 and very well done. All the bases were covered in detail. New crank, cylinders and pistons, pump gone over etc, etc. Runs like a dream and dry as a bone. I just looked at the plugs after about 1000 miles and 5 of the 6 look perfect. Cylinder No.3 though is full of fluffy black carbon. I do all the work on the car except the motor so I have some good skills but have never played (successfully) with the MFI pump or the adjustment of the throttle bodies. Is this a simple adjustment? Just trying to get educated a bit before I go back to the builder.

Thanks, Greg

[stlrj]

#3 ignition wire could be at fault.