I'm only supposing here, but being that they're Keihin carburetors it's probably Keihin's doing, not Triumph's. Also, I've heard that the adjustment is supposedly sealed, kind of like they do with a cheap lawnmower carb. Mine wasn't when I bought my bike new though.I don't get it. Why did Triumph go from a really handy knob to requiring a "D" shaped tool to adjust the idle mixture?