OK, so yesterday on my 13th yard my mower started acting up on me. Let's just say this kitty is a year old. I noticed the fuel filter was dirty and changed it out. Symptoms: back fires once when you give it a full throttle (occasionally) as well as when you idle it down all the way (occasionally). It idles lower than normal and doesn't sound like it is going 100%. When trying to go wide open it cuts the power down and sounds as if you start cutting 3' high grass (engine idle and tone). The cut quality lacks because the engine cannot supply the normal power to the blades as it usually does. I have to mow SLOW and sometimes cut it twice at reasonable grass heights. It used to when engaging the PTO idle down, but now it stays up just a bit under par. IF I Can remember correctly, it only occurs when moving forward, but I cannot remember. The tensioner/idler pulley on the deck seems to be shaking a bit more than normal (blades NEED sharpening, but maybe out of balance or pulley needs adjusting)? It just is not acting right and I have had no problems since this. Things I have tried: I have cleaned the carburetor completely, changed out the fuel filter, added techtron fuel treatment to both tanks (as seen in another thread), cleaned both air filters, cleaned the spark plugs and re-gapped them (had a little smoke colored tint to them), and I think that is all. I have maintained my mower fairly well and by everything the manual says. Changed the oil, filters and keep it greased up. I love this ol' girl (last years model off the floor) and she has treated me well having 180.9 hrs on it. I would love to repair the machine myself as one Kawasaki Dealer even under warranty is 5 weeks behind! I have got to get this thing going soon. I have experience tearing down a small engine and car engine, so I am just puzzled at what might be causing this. The manual says the spark plugs should be changed every 100 hrs and I havent done that going on 200 soon. I don't know if I should do this to do it since I missed that mark or if it could be causing it. Any help is GREATLY appreciated! I have a Walk behind, but I am waiting on wheel drive belts . As we all know, mower down=down time=losing money. Weird that it is a year old and doing this. I am unaware if I cause this, bad gas, clogged fuel filter, fowl plugs, etc. Oh, it did it one time and I prayed it would stop and clear up and it did. It just came back this time. Rain has been hitting us good and grass is growing, so I don't want to get too far behind. Thanks again guys.