I am not familiar enough with this motor to know about restrictions, however, it sounds like you are running way too rich.
When you had a plugged filter, the reason it ran so well just before it died, was that the mixture was leaning out from lack of flow to the carb.
Check that the float in the carb is in good shape. If it is metal, shake it to make sure it has no liquid in it, if it is composite, check for saturation. If the needle valve is leaking significantly, it will leak gas as long as the petcock is on. You sometimes have to look in the intake to see this.
If all of the above is ok, go to the bike shop with your main jet and a magnifier and compare your jet to a new one. If the look the same, try a smaller main jet, but be carefull of going too lean as you will seize the motor.