Now you have a tight connection to the idle stabilizer, observe the motion of the operating rod protruding from it as you open and close the throttle. If it moves when you do this, then the stabilizer is functional. If there is no movement, then the device is kaput. If it works then you need to balance the carbs. A good ear can hear the difference in air flow from one carb to the other. I have always used a "Uni-syn" with a home made adaptor to balance idle air flow.
Once you get all that done, assuming the ignition timing is correct and the advance parts in the distributor are free and working, the stabilizer might work just fine. If not get back to us.