I did a bunch of plug testing and general tuning work on Friday. The motor ran fine on OS P4 and P3 plugs, as well as the O'Donnell 97T. I found out a few interesting things.
80 degree air temp, 45% humidity for the day. Started off with the P4 and dialed in a good driving tune, not on the ragged edge. Temped at 245-250. Put the 97T in and had to richen the top and bottom 3 hours to get the same temp and engine feel. Put the P3 in and had to fatten just the top another 3 hours to get the same temp and feel back.
I stayed with the P3 the rest of the day, then started playing with the bottom end needle exclusively. I'd never really played with that needle before, and was surprised by what I discovered. I was able to richen that needle one whole turn from where I was to where the engine was starting to blubber out of tight corners. I only started seeing a temp change in the engine after I'd fattened up the low end 9 hours. I had no idea the low speed needle's "window" was so large. I finally learned what an engine feels like when it's too rich on the bottom, too. It will stumble for a moment right when you grab the throttle coming out of a corner, then start pulling. If I remember right, an engine that's lean on the bottom will pull for a moment right when you grab the throttle, then fall on its face.
The powerband REALLY improved coming out of corners once I'd fattened up the bottom about 6 hours. I think this was magnified by the track I was on because it was low speed and technical.
The high speed needle's "window" is still pretty small. 3-4 hours between four stroking and super killer race tune on a small track.
I couldn't do any race style pit stops during my testing since I was the only one at the track, so I don't know how the engine would have run after a fuel stop. I still had the incredible idle that I had the last time I ran it though, with the idle only starting to vary considerably once I had made the low speed needle REALLY fat.
Your mileage may vary, void where prohibited.
