Jim, see where the dirt gets compacted between the teeth there, i am calling that a "pocket" and what i do is make that pocket a steep ramp down away from the the side that faces out. So, looking at the drive wheel from the outside you would not see that it has been modified but, if you looked from the backside you would see that the pocket has been sharpen like a serrated knife. Being just soft pot metal though, i would not make the edge too sharp or the drive wheel might wear out very quickly.
Hopefully if you look closely to this photo you can see how i cut a steep ramp into the pocket and just a sharp edge actually touches the drive chain.
