Ok thanks for all the tips......I just think it's very odd that I'm in my second season of flying this plane,with this exact setup,and have never had a problem until now. I would think that if this problem was created by the exhaust deflector,then it must have already caused irreversible damage,because it has run great for all this time. It seems to me more likely that perhaps something got gunked up in the works and caused the sudden drop in rpms. I probably aught to take things apart and inspect them closely.
I was actually hoping someone could explain the blackness on the plug. I figured that was a tell tale sign of some tuning mistake or something. But,since I leaned it out quite a bit to get the rpm's back up after the strange drop-off,perhaps I was simply masking another problem and am now running too lean?