I have a 2002 yz250 and when I change the oil I pull off filler cap and drain oil but no matter how hard I try I only get about 300ml out. What the heck? I can pull the weep bolt also. When I fill it up it only takes 300ml also till it comes out the weep hole. The case itself says 750ml will somebody with the same bike help me out, is that all the oil I will get out or is there a trick to it? Also is there a filter to change also or not I can't find one.
Is the bike vertical and level on the stand when you change it? I actually lean mine to the side nearest the plug. Also, loosen the filler plug so air can come in from the top. Other than that, I don't know.
Just looks like it hasn't been filled up properly in the past, either that or your bike is burning up shed loads of oil. Just measure out 750ml, pour it in, have a good few rags around with your bike, then drop the oil to see how much is left.
quote from my yz250 manual "start the bike and let it warm up for a few minutes. wait for five minute." perhaps the oil was not filled all the way last time?