Having trouble that just started the other day , the engine misses real bad & died once heavy black smoke (not blue not white) came out of exhaust & was very hard to start. Acts like it is getting to much gas or running rich... I changed the plug, airfilter, gas no help seems to start after its warmed up. This model has the electronic gas shutoff on the carb fuel bowl could it be the oring ? I heard something similar happening to others ?