After checking everything else I could think of, I finally cut the muffler off the exhaust pipe...the exhaust pipe and muffler are one piece. The issue is that the muffler is blocked on the inside. So I am going to most likely look for a muffler to replace it.
I used a cutoff wheel to cut around the circumference of the inlet end of the muffler, but it would not come apart. Appears that internal perforated tube is connected somewhere inside. I guess I could cut completely through. Funny thing is, nothing came out when I whacked it on each end while holding vertically, nor does anything rattle inside when I shake it.
Yeah exhaust issues can drive you nuts... I once rebuilt a CR250 thinking the two stroke was tired. Turned out the silencer core rotted and let the packing fall to block the hole. Was pulling my hair until a buddy put his hand over the exhaust and said....there's nothin coming out. I was pretty green back then. Good news was that bike ran fast after the new rings and piston. If I skipped race day, my buddies were fighting over who got to borrow it.