Yes standard gearing is 15 tooth front, 42 tooth rear. See here for the gearing specs I used.

If you install Open Office Aqua (free and open source) for Mac OSX 10.3 and later you will be able to open this .ods MC18 gearing spreadsheet which is the same as the MS Excel one I posted above. Hope that helps?

Also, (in New Zealand at least) Honda did issue all NSR250 R5k owners with a 16 tooth front sprocket as a bit of an "afterthought". I know this, because I owned an MC18 back in 1990 and went into my local Honda dealer to get the 16T front sprocket.
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[color=#808080][size=9]Yes,.. I too know how to waste Time and Money,...