When petcocks off my bike runs better

I wouldn't worry so much about the filter as I would a top end rebuild. Without the oil the fine particles don't have anything to stick to and if it doesn't get caught in the carb it's going straight to the motor. K&N let enough through as it is. Not sure if there is a advanced auto around you but the one here sells the recharge kit for like 13 dollars.
 
At the throttle position of the bog when riding, reach down and pull the choke out a little!

If I it runs better it is too lean, if worse too rich.

You may need to alter the needle setting!