Hello hello out there.
Just curious if this problem was ever fixed for you! I am having the same issues with a demon I just acquired from my neighbor. He was having an off idle stumble really bad like you've described.
He never did get it to work again on his car. Originally, the carb he worked well for him. THen I think he put new gaskets in and it has never been the same since. I did notice that the new gaskets are blue. Does this mean they are HOlley gaskets??? Will they work??
Any more help from BG TECH would be much appreciated.
THanks in advance for any help you can give!