As the fellas before me have mentioned allready its probably piston/rings/cylinder damage due to wear and tear.
A couple of other things to look out for is a blocked air intake/clogged air filter, this will cause the fuel mixture to run very rich, giving you lots of black smoke and it washes oil from the cylinder wall, this will wear out the rings and cylinder/piston thus causing excess oil usage, the worn rings will also allow combustion pressure down past the rings and this pressure will force oil up the breather pipe and into the airbox.
Something else to watch out for is a partially or fully blocked crankcase breather, at high rpm the excessivley high pressure inside the crankcase will force oil up past the rings which will then be burned off in combustion.
Let us know how you get on tommorow.
P.S. looks like im not the only one with mechanical troubles at this late hour, I just got in from rebuilding the gearbox on a 885cc Triumph 
Best of luck and if the Yam dealers in Toulouse are half as helpfull as the ones in Rouen then you'll have nothing to worry about.
Last edited by adrian74; 11 Sep 2010 at 13:41.
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