FWIW, Kadrons are notoriously hard to dial up. My car came with a set and I just sold them and bought a set of Dellorto 40's that were "plug and play". The posts above are spot on. Intake leaks will do it. With my Dellortos I had occasional backfiring on deceleration but that was after 15 years of them being installed and it ended up being a plugged jet on cylinder #2 so that cylinder was being cancelled occasionally. After cleaning up the carbs everything went away.