I have a Speed Demon 750 mechanical secondary carb that i want to switch to a vacuum secondary carb, is this possible? or just a waste of time.  I swithced to a automatic, and i thought that it would be a good change for the motor.

Jordan

Sorry, they can't be switched.  The mechanical secondary carbs don't have vacuum passages drilled between the primary venturi and a mounting boss for the vacuum diaphragm housing.  In fact, the mounting boss may not even be fully machined.

It's probably cheaper to just buy a vacuum secondary carb, even assuming the base casintgs are the same for both types of carbs (which they may not be).