Cleared the ground for a brief period today. As far as the airplane is
concerned, everything is good. CG seems to be right on the spot. Much
better as it was 12 years ago at the first flight with the SOOB.
Here is the reason why it was not a flight. A few days ago when I
started high speed taxi, as soon as it picked up air speed, the engine
started to sputter and almost cut out totally. This was at the same RPM
as at a run up, where it does not do that. With a wiggly tail dragger as
the Avid is, there was no way reading enough instrument for making a
preliminary analysis. I recorded the instrument panel with a GoPro at
2sec intervals.
Looking at the first pictures, the answer came up right away, increasing
pressure under the cowl where the intake for the engine is located. Like
the EGT shot up over 1600 just before the sputtering started. Since my
radiator air is going to the outside of the cowling, there was no impact
on cooling. Btw cooling is really good. At an OAT of 95F, oil and water
stayed at around 170F no matter what I did.

For todays runs, I taped the inlet around the prop hub shut. Sure
enough, the sputtering occurred at higher airspeed, and was not as
total, however, EGT was still going to around 1600.

The conclusion is, I have to open the cowling exits a lot.