Tuning a Demon Carb

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I ran a Demon on a BBC & had no issues with timing either. My initial "guess" would be that the carb is too big & they have installed oversized jets &/or nozzles to compensate. Is it a Vacuum Secondary carb, or double pumper?

If you do a carb size calc online you'll get a pretty good idea of the size Carburetor you need. I ran a 600 double pumper on a big block chevy that was in a big old cadillac with 2.92 rear gears. That little carb gave the motor a nice tight bottom end like nothing else would(I also ran a 750 & an 850 on that motor). Since it rarely saw much over 5k rpm, if it saw that, there was really no need for more carb. A Cobra is obviously a different beast. However, if you examine your driving habits & install the smallest carburetor the engine can reasonably run, given those circumstances, you will always have a little more snap in your acceleration & the possibility for better fuel economy.
Keep in mind that if you go too small your engine wont be able to suck enough air/fuel through the carb at high RPM & you will not have the power up in that range that the engine "could" produce. It's all a matter of how the car will be driven.