82 Vanagon with original type distributor and Weber carb.

According to St. Muir air cooled engines should be timed using the static
timing method.
OK I'll buy that.  So out with the voltmeter hooked up to condenser wire,
ignition on.

Move crank pulley slowly, voltmeter jumps to 12V at 7.5BTDC after some
adjustment.  *Tighten distributor*.

Start engine, idles immediately, dwell at 50, idle adjusted to 925.  All is
well.  Or so I thought....

So I turn it off and re-check where the timing mark lines up.  It will sit at
8ATDC.

This keeps occurring.  If I set the timing, then start it, and then re-check
it, the timing is off.

What gives?
Paul
'82 GL