I also prefer the Mikuni carbs because they have more circuits to adjust. The PE, PJ, PWK, Air Striker do not have the ability to change the Air Correction Jet, Needle Jet, or the size of the Float Valve Seat.
Needle jets ware out in all carbs. This is the main reason that needle selection varies among those that have the same engine package as others, but need to have a different needle to compensate for the ware in the needle jet and needles. Another reason that Keihin needle jets ware out so quickly, is they are using a bronze needle and a brass needle jet. Common engineering practice is not design mechanisms using similar base metals for components that have two surfaces that slide over one another.
Mikuni uses a brass needle jet and a hard anodized aluminum needle. Using dissimilar metals greatly reduces the ware on these two components. I cannot remember when I measured an old Mikuni needle and found any ware when compared to a new needle. When I measure a Mikuni needle jet and find ware, I just replace the needle jet and not have to spend $200.00 worth of time searching/tuning for a new Keihin needle that will restore the performance to what it used to be when the carb was new.
I have to use a small bore gage to measure needle jets. You cannot use gage pins to check the ware in needle jets, because the needle jets holes become oval in shape.
