a thought on the shroud/case...
have you ever had one of those high velocity fans or air filters? they work best with their casing because the shape of the case directs the air around to where it should go... the air filter either suck or pushes the air through...
the shape of the case allow the fly wheel to create a vacuum sucking the air through and around the engine, no case no vacuum effect, little to no cooling of the engine. that little fly wheel provides way more air flow around the engine than the movement of the bike ever could.
excess heat makes vibration
excess vibrations make a dead engine.
no case means soon you'll have a dead engine
just my 2 cents