could someone please tell be the oill type and fuel mixture for an 87 yz250

although not familer with the bike myself and not having a manual that old for it I did some surfing for the answer.

The ratios are from 32:1 -> 40:1 -> 50:1 with the popular choice @ 40:1.

Going on pure 2-stroke theory (yes I was a mechanic) too much oil will cause rough running and foiling of the plug and baffle. Too little oil will cause extra engine wear and overheating (yes the oil does produce a cooling effect on the engine). If you cant get a definative answer then I would go with 40:1 and keep an eye on engine performance (power will fade if overheating) and the state of the plug (or oil dripping from the exhaust).