Usually when an engine starts to misbehave there are two things to check. The first and easiest is to put in a new plug. Just because a plug glows with the battery doesn't mean it'll keep glowing without the battery and the way you said it seems to be running rich indicates the plug has gone bad and is acting like a very cold plug. It doesn't really matter if the plug has an idle bar or not so long as the heat range is OK. The second thing is to try some fresh fuel. Of course, if it's suddenly lost compression then it's a different ball game

All engines turn counter-clockwise from the front and all of them have a normal right hand thread for the prop nut. As Missileman said, the normal running torque of the engine tries to tighten the prop nut but when you use a starter then you're putting torque on to it in the other direction so the nut can come loose sometimes. A couple of times I've actually spun the prop loose when hand starting but that's because it was a wood prop and they compress a little bit when new and that loosens the nut.