Reading down through the above, I got cornfused, so to set some things straight (at least in my mind)...
1. If you've got a Demon carb, you won't have a SCV to worry about. Just make sure your distributor isn't a SCV-type dizzy, or you'll never get it right.
2. Manifold or Ported vacuum, it only makes a difference at idle, and that's it. As far as the vacuum advance "running out and the centrifugal taking over", that's not how they work at all, you can have either, both, or none operating, depending on rpm and load. I firmly believe in straight manifold vacuum, the only reason the makers used ported was to increase combustion temps at idle to reduce emissions. As far as driveability, an engine with ported vacuum advance may feel peppier, but it's actually not - it's just catching up to where a manifold-vacuum advanced engine was all along.
At any rate - It looks like you've got two separate issues to deal with:
1. Hesitation - sounds like that carb needs looking at. If you can turn in an idle mixture screw and it doesn't affect the engine, something's wrong. You should be able to turn each screw in independently until they just start to drop the idle, and you should be able to see it happen on a vacuum gauge. Tune each one for the highest possible vacuum level, and you're there. Since one isn't doing much, I suspect trash inside the carb somewhere.
2. Stalling on left turns - is your Demon mounted sideways, or is the float bowl to the front? If it's sideways, you may be experiencing a momentary flooding on the left turns. I had the same stalling/hesitation with my H/W 5200 until I dropped the float level WAY down low.
