One of my theories was that the transition circuit on your secondaries was very lean, and so when you first tip into the secondaries the AFR rises a bunch. However, given your current IFR and IAB sizes, that does not seem like the most likely culprit.
The secondary AP can certainly be part of the issue if the secondaries are starting to open, but given how long the leanness persists, it seems there may be something affecting fuel flow in the secondaries with small secondary blade openings. At the moment though, I don't have a good theory.
Look forward to your further testing! Will you test with the secondaries disabled?
