The bike needs a top end job. Oil is getting past the piston rings causing the bike to smoke. The best thing to do would be to have the cylinder bored then install a new piston and ring set. While the top end is apart, have the mechanic re-seat the valves. The air filter is filling with oil because of the compression getting past the rings. Maintain the proper oil level in the gear box to lessen the problem. You may want to find a new mechanic. This is basic information any competent mechanic would know. I am not being ugly, I just want to help you out.