mavt

If you are using a 28mm, its a little large for a TY 175. The Keihin copy, OKO 24mm works great with a 115-120 main and a 48-50 pilot. Use the JJH needle in the top slot.

If the idle had been lean with the stock #20, someone may have switched to the #30. If your bike four-strokes when you blip the throttle a little, that is a sign your #30 is too large. The #20 is the correct pilot jet, so my best guess would be the pilot circuit became a little clogged so the #20 was swapped out for the #30. If the circuit itself is clogged, the #30 won't make a difference. I'd clean the idle circuit and put a #20 back in and see how it runs.