Truck Repair: Carburator, cold drizzle, gas mileage

Question
I have a 86 Dodge D250 Truck with a 318 and a Holly Single barrel carb.
Most of the time it runs great !
When it is Drizzel rain and especialy when it is COLD Drizzle rain. It starts Great, Runs great, but about 1 mi down the road, about the time the  Choke should kick off, it starts running Soooo bad I cannot take my foot of the gas pedal. It will Die and be hard to start. but it does always start again. I checked all the choke linkages and they are clean and free not binding.
(Note: the gas mileage has never been better than 8 Mpg) The exhaust pipe normaly has sooty Black coating. The Plugs seem to look a little wet but are burning good, not black & sooty. Performance seems good. I only live 3 miles to work so it never really gets warmed up very often.
Sorry for all the jabbering just wanted to get you all info needed.
Thanks in advance.
David

Answer
If its burning black like that it sounds to me the vehicle is running to rich. You should have the timing checked on the vehicle, and your carb cleaned. You may want to buy some carb cleaner, and try that first. Otherwise, it sounds like a timing issue to me.. Ty..