One thing I failed to mention is I am using a modified needle valve.
When I first ran my bokabob I noticed that the needle valve setting was extremly touchy - very sensitive - very course resolution as far as setting the flow rate.
After dissasembling the needle valve (which came from Lowe's), I found that it wasn't a "needle" valve in that it did not have a long tapered needle that penetrated through an orfice as I had envisioned. It had a tapered seat with that mated with the tapered end of the stem to stop the flow. The thread pitch on the stem was 32 tpi.
I drilled out the stem, then fabricated a long tapered needled with a shank size to create a press fit into the stem.
I drilled out the seat, and then fabricated a new seat to press fit into the hole I drilled. The new seat had a small orfice for the needle to penetrate.
Result was much better resolution in adjusting the flow rate. However, it did not overcome the variation in flow rate which Harry attributes to "needle creep".
Thanks for your comments.