Can safely be derestricted to 21hp. Allspeeds and bigger main jet will let it do 90mph but loss of power below 6000 revs. Ability to wheelie’s a sign of a good engine, as is a slick gearbox. Rebore at 35 to 40k. Check rear suspension for wear, swinging arm rusts, calipers seize. Neat way into the learner game and useful, when tuned.