Exhaust Manifold Was Glowing a Little

[Idaho Brett]

Finally got my Model A to stop backfiring and I was feeling pretty good. I got out to look and listen to the engine and bask in my glory when I noticed the exhaust manifold and exhaust pipe clamping area beginning to start glowing orange/red a little. Of course I immediately shut it down.

What's going wrong? What do I need to fix or adjust? Thanks.