it's not easy to test air leak in motorcycle engine.
the best way is to put out the pipes and carbs,
blank the exaust and pressurise the cranckase with an adaptater in the inlet manifold (hand made).
I use a sthill pressure pump to do that

the piston must be at BDC and the pug in
a vacum test is also important to test the cranckshaft seal

you can find the leak with a special spray
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