have you checked the inside lip of your clutch fly wheel ? If you take yoru flywheel off and look at the collett and it has scuff marking on it there is a chance the collett has gouged out a bit of the flywheel material .. It will feel tight when you wrench on it but under load it will slip indipendantly of the crank and seem like lean bog.

Ok So take off the flywheel , look inside where the collett goes and see if you can see a lip .. if its there get a new flywheel and collett and tighten the suckker down hard !

If thats not it then you have to ask why is the engine lean bogging ? It will only lean bog if its starving for fuel. or if its making power but cant get it to the wheels because of something in the drive train.

Lean bog can develop over time if the engine was run in cold
Any sort of Air leak in the tank , pipe , seals , pressure line
HSN needle dirty
Head bolts loose


I think the problem is outside the engine .. check the clutch first ..

hope this helps

Cheers MM