just put a pair of vise grips on it and unscrew it.
I have an air filter and adapter that i'll sell (only installed, never run). I'll take $24 shipped for them. No paypal.
They'll bolt right up and get rid of the whole airbox. It also makes rigging a throttle way easier. I bought that set up and then decided to go with a mikuni so i no longer need the adapter and filter.
Here's a pic of it installed. The filter is mounted on the adapter. If you want it pm me.