Hi ,there, ,is the RT100 , not the DT100, ?,, not familiar with it,, look under the seat for oil tank, and the R/h side cover should have pipes going into it [ pump], if not its a Pre-mix, [ off roader], 30/1 is the ratio . near as,
http://yamaha-enduros.com/index.php/100cc-specs/67-74-80-dt100-a-g-specifications