I'm clueless about engines so please be gentle...

Have a DA50 in my H9 Extra 260, since last fall but most of the flying and gallons of fuel were ran through it this summer. Within the past month, it has started to run less reliably while ilding on the ground. For example, I'll get it started up and sounds great, transition from idle to full throttle is good. But if I bring it back down to a high idle and let it sit there, it will eventually quit abruptly... Alternatively, if it idles for a while and then I give it a slight amount of throtle (one or two clicks), it will also sometimes die.

Similarly, runs great in the air but once I'm on a landing approach (flying idle, not low idle) and having landed, it will sometimes quit within a few seconds of taxing back to the pit area.

Also, my spark plug seems to have a lot of nasty carbon on it. I've been taking it out regularly cause I'm often flooding the engine (plug soaked) at the beginning of the flying day.