Timing Jump on 165/TPI System

[Craig Moates]

Folks,

A question:

With timing control connector disconnected (ie. setting timing on a
165-based TPI motor), timing should sit still, which it does for me at low
RPM. However, when I idle it on up to say 2000 or 2500, it seems to advance
like 12 degrees or so, instantaneously, and hold up there until I idle it
back down. Then it jump-returns to the previous value. This is all
timing-light based. Any thoughts on what is being seen? There's about a 1-3
degree drift on idle-up, probably from timing chain stretch, but that's not
huge.

Anyways, fishing for thoughts. It's not problematic, just would like to
understand what's happening and why.

Sincerely,
Craig