jetting a 250 desmo

Does anyone know if there is a minimum size for the main jet on a 250 desmo?

I currently have a 105 but the plug is still oiling horrendously. It had a 120 which is apparently about right for a 450! Since tried 110 and 108- both oiled horrendously. Is there a lower limit? I’m wondering about simply buying everything from 95 up! Or should I start at 75???

Many thanks

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Hi Ignatz, forget the main jet, 105-110 should be fine, the problem is more likely to be needle jet wear or oil passing guides etc, is the plug fouling matt black or shiney, shiney is oil. does the carb drip fuel , the float can stick or be too high. What carb , what slide? Most of the running is on the needle --needle jet.