It looks like a old Ryobi gas engine conversion from when Ryobi was still making engines in the USA.  It looks larger than the 35cc (1.9 cu in) Ryobi gas engine conversions that were made under the Evra brand label.  But the steel prop driver looks the same as those that are found on the Evra engines though. The flywheel is quite similar too, but the extra stuff was removed or machined off on the Evra engines.