Do a search on some key words and you'll find anecdotal information which varies from 20-80 miles.
There isn't an answer that is THE answer. Too many factors. A recent thread regarding hare scrambles 'mileage' had input from some that (mileage wise) would take two tanks of fuel at a local HS event.
At least you have a reserve (well 95+ do..don't know about '88).
Any checking on this forum will show you that a whole lot of bikes are jetted poorly (too rich, generally). You should check it anyway (welcome to 2-strokes!), but if range is an issue, you REALLY should make sure it's close.
Have fun!