I used one for 5 1/2 years 15,000 miles and about 110 passes, I took it apart changed the spring to a light one and bent the tabs until I had the advance where I wanted it still have it sitting on the shelf.
Man I remember helping my buddy with his 6 pack what a pain! Make sure the carb and gaskets are lined up properly and tune the center carb with the linkage disconnected, we had the same issues of unstable idle ,it takes time but once you get it it works pretty good until you build a bigger...