This is a common problem (on all 2 strokes), sounds like your too rich also, where are you located? Altitude can have an effect on mixture. But just take off the head pipe and redo the hi-temp silicone sealent around the pipe flange, that can take care of the leak.
You dont have to take the oil injection off. Athough it is a good idea. Doing a oil injection block off will not stop the leak, but when mixed properly will assist in leaning out the fule/oil mixture.