I just had a similar issue with a 83 SC. Went through the CIS pressure testing and found my rebuilt WUR was a little out of cold spec. (to rich) But the big problem was actually my base timing. I had engine work done and the car was returned to me with the base timing set to 5 ATDC instead of 5 BTDC
. Reset timing and now have perfect cold starts. Your issue may not be timing, but it is a quick thing to check and remedy. Tony and Bob will not steer you wrong with CIS issues.