eBay purchase turned out to be broken despite being listed as good working order. turned out to be a broken valve adjustment screw which are no longer available. i had an idea that the o.s version may be compatible and Just engines confirmed the fix , now the engine runs very nicely. the vendor of the engine agreed to pay for the parts needed and was very helpful. the super custom four stroke .52 cu rc model engine is destined for a 1/5 scale piper cub.