Get a meter and test the bystarter. You should have no more than 10ohms between the 2 pins on the connector. Did you set the air screw at 1 3/8 turns out?
still, that is dangerous. you should AT LEAST get a sponge that will fit in the airbox (or cut down a larger one) and soak it in gear oil. But getting a real air filter would be best.
Sounds like you might be getting to much oil, not enough gas. You said the headlight dimmed...your mag might be going, that would also give you a weak spark. Get it started again and measure how much voltage you have going to the batt. You should have around 12.9-13.4 at idle. Check all your grounds...A lose or dirty ground connection will mess with ya' too. Change your plug again(when working on 2 strokes always keep lots of plugs around)