Amsoil Motorcycle 10w40, works extremely well in my Wiender engine.
tabernash125: I'm not a fan of 20w50 oil even in air cooled engines, especially if it's a fairly low hour engine. Tolerances on new engines are very tight and don't require the ticker oil of yesteryear. I have tried several different oils in my daughter's 125 using a IR heat gun to gauge how well the oil is doing in the engine, Yamalube Racing 15w30 actually showed the lowest temperatures after a race, but that oil doesn't have enough zinc and phosphorus to protect the cam and rockers in her built racing engine. Amsoil has shown a slight increase in heat over the Yamalube, but with a significant amount of anti-wear additives to protect the cam and rockers. That's the oil I have settled on.