Timing Jump on 165/TPI System

[John T. Martin]

My  $.02

That is a normal condition, also a test for P/U coil signal strength. The
advance is triggered by the P/U coil signal amplitude, not RPM. It is a back
up as I understand it, but a good test if you suspect a weak magnet in the
dist. We had a run of K engines with shaft problems a while back and in
bypass (est disconnected), 2500 rpm the advance was not triggered. Also the
weak pick-up signal affects idle quality.
-----Original Message-----
From: Craig Moates <craig.moates at home.com>
To: gmecm at efi332.eng.ohio-state.edu <gmecm at efi332.eng.ohio-state.edu>
Date: Saturday, January 08, 2000 9:08 PM
Subject: Timing Jump on 165/TPI System


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