Most of the OPE engines create rated HP at 3600RPM. I recently adjusted the governor on my JD235 to 3600, per the manual. It was down to 2800! Most likely due to the governor spring rusting and getting weak. I don't often need to run the eng at full RPM, but it's nice to have when mulching leaves, as it does a much better job.
NOTE: I think this thread belongs in the Lawn Mower section, not Motorcycle.