[decooney]

Did you change the jets in the Demon carb? If so, what were they before and what are they now; primary and secondary.

What # discharge nozzles are on the carb?

What are your idle mixture screws set at now? You can turn/count the turns in and start from scratch again too...

Are you sure you don't have some sort of a vacuum leak somewhere?

Did you run the car with this same engine and carb during a previous year of colder months, and did it do this then?

...just a guess, but I'm wondering if the popping you are hearing is a lean condition til the motor warms up just a tad...

Check your fuel pressure too. What is it?