2013 Laser Z with Kawasaki FX801V engine. Mower was fine last week, went to start today seemed to be low on power and bogging down when PTO engaged. Replaced fuel filter took fuel cap off when running to check vent, no change. Plugs been cleaned and good. Started it up ran the same way then started bogging down and smoking. Now when trying it will not start and backfires some. Bad gas ? It is getting fuel but seems to be dark looking.