Cannamore is right...in a way!..
Your correct in your assumption our "humid cool mornings" might be troublesome here!..I have a carb icing dilema in every GM vehicle I've owned,whether it was a SBC,BBC,or a six banger..Throttle bodies freeze up just like a carb will under the same conditions...thus the factory coolant passage to "de-ice" it,and the hot air pipes going to the carb from the exhaust manifold,and the heat riser passages under the carb in the intake manifold....
Icing can,and often does, occour at temps as high as 50 degrees!..its most apt to occour between 28-50 degrees..here,its not that often we get down to,or below zero--but when we do,the air is usually bone dry,and I've rarely experienced icing on those kinds of days...but we have many 30-50 degree days with rain,drizzle,snow,and fog,that are the pits if you have a "cold blooded" carb or throttle body...
My 79 C10 suffers a lot from carb icing,the Edelbrock carb and its spacer never warm up enough to vaporize the fuel well,or keep ice off the throttle plates on cool damp days,unless I use manifold vacuum to hold the heat riser (EFE) dewhickey closed,and run a stock air cleaner with all the factor hot air plumbing working correctly..then it runs great..its a dangerous situation to have a truck that stalls every time you take your foot off the gas--and mine does just that if I try using the Edelbrock "open" air filter,and no "heat" to the intake manifold..
I never realized how much better an engine runs with properly atomized fuel..that "hot spot" is a nesessity,not an option really..
I have found you can "fudge" things by using a few cans of Isopropanol alcohol dry gas,if your not into keeping everything stock...it keeps the ice from forming,and freezing up..
