Haha, I did exactly what you did, I swapped a few domes/piston assembly from spare carbs... all the same story. Sorry, I didn't watch the a/f ratio while this was happening, but I had the manifold tapped to measure gas-temp on cyl 1 &4 . While this was happening, the temp was higher on the dropping side... could be something about the mixture moving the wrong way. With the joining section blocked and linked with a smaller tube, the temps seem more even. (but still not the same, could also be my funky carbs.) I haven't put the car on the dyno yet after blocking the section, but the engine seems abit more responsive now though... and with ex-gas temps close between 1&4.

Hope this helps.

Oh, a quick question... I have some spare stock rods for my b20, but thinking about taking it through "sub-zero" process...(let it bath in liquid nitrogen for a few days...haha. It's free anyways...I love uni!) Any thoughts if it'll do any good, planning on doing a complete rebuild soon.
And also, should I get the rods shot-peened? I have access to a super-drill machine...
Any thing else I can do good for my rebuild?

Cheers!