Are you sure it isn't a 175 main?
If you don't see any markings on the needle it may be a jetting kit where the markings were removed to keep someone from copying it. e.g. old LTR jetting kit. This is a keihin needle.
If you don't know which needle it is - I would pick up a needle suggested elsewhere here - e.g. "suzuki needle" or "yamaha needle"...
With all replacement (improvement) needles - you typically run a richer pilot jet and reduce idle setting to better separate the carb circuits (high/low). My experience (which is a bit dated) is that you should see a 42-45 pilot - maybe a 40 - but definitely not a 38 if things are set up "well" (given conditions are not extreme).
jeff
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