80 SC Running Rough?
 

I have a friend with a '80 SC who have not used the car for the last 3 months (parked outdoors).

The car starts up one click, idles fine but when I start driving off it seems to run lean / rough because the spark plugs are whitish/greenish (when pulled out). It back fires from the intake air box. Condition is worse when cold and improves after 15-20 minutes of driving. Problem is between the 2000rpm - 4000rpm.

Sounds like an air leak, check the air box for cracks.