I did some work with Burlen a number of years ago trying to fit Amal carbs to the "New Triumph Bonneville" (an interesting journey) and learnt a lot about old British Carburettors.
One piece of advice I thought was a sales pitch, but realised wasn't, is that once the body of the carb has worn it is better to buy new, not re-manufactured. A new 2014 SU will be made to tighter tollerances than the original new SU, made of better alloy and will simply work properly.
I know there is a certain attraction to makeing the old one work, and many people ride this wave offering all sorts of services, but the soft alloy used in the 60s and 70s wears, not just the piston bore and the throttle spindle bearing surface but the internal airways. They corrode and get bigger...and once they are no longer as they should be it is game over.
SUs were better made than Amals, btw...old 70s Amals are just horrible.
