Greg, it seemed to be a sort of given that as Amal advanced in carb design, the quality fell off; so a Pre-Monobloc is better than a Monobloc, which in turn is better than a Concentric. Of course, none of the street carbs had/have the quality of the race carbs like the TT and GP series. Personally I quite like Concentrics, they're a very simple carb (ideal for me!) which is easy to tune. But their biggest advantage is comparative cheapness, so when they start to misbehave, it's best to just replace them. This was done at purchase of my Bonneville and Commando as a matter of course, so there's no reason to think it's not applicable on other bikes. I have a box full of worn Concentrics in the garage, I'm never going to use them so I often ask myself why they're still there (just too idle to get rid of them?)! What makes me laugh is seeing boxes of old sh**ged Concentics at autojumbles, who would buy them and why?