all engines do comsume oil ,but its not refered to as burning oil until its excessive and usually causeing smoke,as when rings wear out and valve stem seals fail.New engines often have rings not completely seated and consume more oil early in life.old engines consume more oil later in life as rings wear and as carbon causes them to stick in there grooves.AS for air air cooled engines,evaporation is a big factor.meaning,more extreme temperatures cause oil to vaporize more rapidly and get exausted after combustion,and also leaves through case and rocker vents.My 08xb has been the same as my 99s and the same as almost every aircooled motor ive owned.I just top the things off and ride the hell out of them.unless your crop dusting,dont worry be happy!