[1991 GSXR 750 BST38 Super Rich.]

No wear on the needle/emulsion tubes

Longish post, so I might have missed it but- how many miles on the needle jets?

Once they start going obround (and even barely visibly so) you'll be chasing your tail forever.

.

[GSX1100 carbs.]

I've run K&N duals over the years, and always had good luck there but the prices have gotten pretty steep.

This time around I picked up a set of individual-style pods from Gixxerzone  http://gsxrzone.com/airfilters.html  and the fit/finish are very good for the money.