Originally Posted by MassiveMods

Sounds like a front bearing leak to me .. New or not sometimes the front bearing is faulty from the manufacturer. try to move the rubber seal with your thumb nail , if it moves then you have a leak ..

What happens is once the crank case expands it relieves pressure on the outer seal.. this causes air to be sucked in through the front bearing as opposed to through the carb ...

Hoep this helps ...