Hi, i bought a, 81 RC last summer, had no problems with it til it sat for about 2 months, had a no start issue, found it to have no spark, so i replaced the ignition coil and it fired right up, ran fine until it got cold (im in Colorado) and any time its below about 32 degrees or so it wont start. VOM says its getting voltage into the ignition coil and into the distributor, but im getting no spark as tested by a spark tester. Ive even had it in the shop and the tech beat his head against it for three weeks, replaced the cap rotor and finally the whole distributor and still the same problem. it would sit outside all night and refuse to start but after about 20-30 minutes in the heated shop it would fire right off.
Ive tried everything i can think of and am at a loss. Any help or ideas on where/how to chase down and slay this gremlin would be greatly appreciated.

 

I am going to take a guess that it is a 2 bbl carb? Been a long time since I dealt with a carb but if I remember correctly, on the passenger side of the carb is an auto choke that will work based on an electrical charge to heat up and allow the choke to open to allow starting. Check that, if need be replace with a manual choke with the cable going to cab through the firewall.
Also check the fusible links on the drivers side near the fire wall.
Hope this helps.

 

have they checked the ignition control module? the ignition system on these older vehicles are fairly simple
4 pin single ballast resister system

5 pin dual ballast resister system