[Tom Kirkham]

I have never worked on a Demon carb, but if it is like a Holley you might want to check for a vacum leak. An easy way to check for a vacum leak is to spray starting fluid around and see if the engine changes the way it runs. If the engine is running lean it will speed up, if rich it will slow down.

Yes you want to set the idle screws where the engine is at the highest RPM. However, if the RPM gets to high you will be out of the idle circuit and will need to turn down the idle speed (by closing the throttle shaft).

How well does the engine run?
How does the engine idle?