Ok, I got a fan installed in the outdoor exit pipe and the whole thing is drawing very well now. It is clear that the mistake was not knowing that elbows need to be counted as five feet, and having way too long a pipe. So, next summer, I'll back up to much less pipe and re-channel the exit pipe out the west side of the tipi, reducing the length considerably. I could just leave it with the electric fan, but do not want any dependence on high technology to stay warm in the winter. I get the electricity now from solar panels. A few years ago, our solar system took a direct hit from lightning (yes, we have all the grounding recommended) and had between two systems - my son's and mine - $16,000 in damage. Without insurance and an existing grid, we would have simply and instantly lost all electricity. Since I fully expect total collapse of civilization, I never count on any high tech stuff continuing. I will enjoy it while I have it, but learn to live without when I don't.
Thank you very much, all of you, for your input and education. I wish I had presented a diagram off the plan before doing it. Oh well, live and learn.