Well that's interesting, since the only thing that should happen is an increase in idle rpm because you have removed the vacuum source that is retarding your ignition timing below 2400rpms (these engines love advance) which means that something else is out of sync/calibration here. These speed switches my not be the problem at all. Before sending off for $145.00 a piece for rebuilds there is much else to check. 1) Check valve clearance. 2) Remove plugs, what colors, black, brown/tan, tan/grayish or yellow shiny glazed? 2a) Warm up engine, disconnect throttle linkage @ IP to cross over shaft, when disconnected push down on the separated IP linkage. Do rpms increase and run smoother or decrease immediately? Push down on the ball end of the crossover shaft, do the rpms drop immediately followed by snapping and popping or do they increase? Get back to us first, then if necessary,3) Follow the instructions of the linkage tour. It all starts here, the relationship between throttle position(butterfly) to IP linkage(fuel delivery) must be correct. 4) Back to basics, set points/ dwell, and ignition timing,(is timing rock steady, or wandering all over the place?) check integrity of cap, rotor, plugs, measure, resistance of each wire, and check coil resistance. Then we will know more. Best of luck, its not that hard
