I agree with Dave on the timing. The glowing headers suggest to me that the timing is retarded. I have seen this happen several times on new engine start up. If you are following cam break in procedure to run the engine at 1800-2000 rpm for 30 minutes, make sure your timeing is in the 32-35 degrees total timing at that RPM. if you don't have a way to do that with your timing light or a tape on your balancer then set it real quick at idle at about 6 degrees then make sure it is advancing as you rev the motor up. What you think is a lean condition may not be that at all, just late timing.

It's something to check before trying to dump extra fuel in there.

Pat