I used to run gear oil in mine but I found that it makes the trans bang when putting it in gear from neutral. It is a little too thich and doesn't allow proper disengagement of the clutch. Use a motorcycle transmission oil, not regular car motor oil and you'll have many years of care free riding. Also the capacity is 800cc which like 250r man said is a little less than a quart. Oil is cheap so change it often.

 

Thanks for the info. I used some yamaha trans oil for now.