Check out this thread about the subject:
http://www.kiwibiker.co.nz/forums/showthread.php?t=104079
In particular check out this post by peasea:
http://www.kiwibiker.co.nz/forums/sh...5&postcount=14
Where they refer everyone to this article:
http://www.vfrworld.com/tex_vfr/tech/oil.htm
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