Demon Carburetor issue

All the Speed Demon's I looked up in a quick search shows they used at least a #75 jet in the primaries. I'm not sure you'd have to go that far, but I think that at least a #74 would help. The fact that this is mainly from a cruise situation leads me to believe that the primary jet is the culprit and not anything to do with the accelerator pump system. I am also assuming that this is a vacuum secondary carb that you have? Once the drivability side is corrected, I think the secondary jetting may also have to be addressed. Any other info you can give us will help, and while I don't think it's related to your current issue, I hope you're at least running the initial timing in the teens.