ok im new here but, have a pretty good knowledge in 2 strokes, so i will try to help, first it probally not the plugs you could try a hotter plug, if you run a 9 try a 8, use NGK!!!, if that dosent help check to see you dont have a stuck float in the carb, old gas, will stick it causing it to flood and foul the cyls, i really doubt its a oil inj problem, once their adjusted they stay pretty good, id be looking at the carb mostly, it usally the culprit, but check to be sure you have good spark too it is also possable to have a elec problem that mimics a carb problem, should have a hot blue spark, try this first and let me know.