Paul, I could certainly believe some reversion below 2500, but the overlap really starts working by 3000. That doesn't explain a rich condition all the way up to 5K. My conclusion is that the tubes are under emulsifying -- simply not mixing enough air into the gas before feeding it to the main jets.

The tubes get the air through the air correctors (obviously you know this; I'm stating it for others' benefit). Normally we think of main jet changes impacting the entire main circuit, while the ACs mostly correct the top end. But what if the ACs are not just undersized, but grossly small? What if the tubes simply can't get enough air overall?

We tried 165, 170, 175 and 180 jets -- a pretty wide range -- and while we saw the effects, they didn't make a huge difference, mostly visible as A/F changes around 5K rpm.

So yesterday I put back the F2 tubes, which had previously clearly given the best drivability, and I put in 210 ACs instead of 160...

The car is transformed. The progression and circuit transition is seamless. It pulls smoothly at any throttle opening from any rpm, which it has *never* done properly. The plugs look right and I can't detect any detonation at all. It feels much quicker yet and it's *much* easier to drive.

That puts me smack on the recommendations found on this site:

http://members.aol.com/dvandrews/webers.htm

42mm chokes (for 2175cc and power peak at 7000)
60F8 idles (result in mix screws 3/4 turn out, correct for 48DCO/SP)
170 main jets (choke size x 4 = 168)
F2 tubes (for 543.75cc cylinder displacement)
210 ACs (main jet size + 50 = 220, but 210 is the biggest I have)

I plan to dyno it again in a month or so, fine tune this and get some new torque and HP numbers, but it's definitely turned a corner in the right direction.