I really don’t see a problem. An engines ability to handle a higher octane means it’s less likely to suffer from pre-ignition when using it. In small air cooled 4 strokes this could happen anytime which would mean IMO, you may be better off. You’ll notice an increase in power only if you could adjust the timing to take advantage of it. Otherwise, you should notice no difference or a slight improvement in performance IMO, if the motor was designated for 87 octane use. Air cooled motors seem to be so variable in temperature, you have much less control over pre-ignition then water cooled.