Last year when I got this, it wouldn't run at fast idle unless choke was on. I replaced the carb, fuel, filter, etc and it ran great for the rest of the year. This year it ran fin until about a month or so ago and now to run at fast idle, it runs rich, with a bit of black smoke out the exhaust. If i slow the idle down, it runs smooth, just less power when mowing. Plug looks OK, just black and sooty, I added some Stabil and it helped a little, tried draining gas and using fresh stuff (no ethanol) but still running rich. Got a new air filter and another set of plugs to try next but open to ideas.. I suppose a different carb??