timing advance

[rhughes@domain.elided]

Hey Harvesters,

I'm finally back online and caught up with my digests, and I'm jonesing to
talk IH.  Be prepared for an all-Rob digest.

Over the weekend, I finally got around to using the timing light that I got
for x-mas.  I'd put it off, thinking that adjusting the timing must be
really tricky.  Well, just like most projects, it was worlds simpler than
I'd feared.

The timing had been set at about 2 BTDC, and I slowly increased it to about
12 BTDC.  Of course the idle speed went way up, but I got it back down,
heard no pinging, so took 'er for a drive.

WOW!  I feel like I'm driving a corvette now.  The off-the-line throttle
response is *way* better.  For the first time ever, I spun the tires at a
light!  It does seem like I have relatively less power later on in the
throttle -- which, from my limited understanding of timing curves, makes
sense.  I've just moved the starting point of the curve over, I haven't
changed the curve itself, right?

I do have a few questions:

1) I've heard no pinging under any conditions yet, and that's with 85
octane gas.  I'm a little worried that it is pinging and I'm just not
hearing it over road/wind/engine noise.  Is that possible?  Could someone
describe the sound of a ping (it sounds like a "ping", duh) for me?  Is it
impossible to miss?

2) I checked the mechanical advance, which seems to be working (it
advances, anyway).  When I applied vacuum to the distributor diaphragm with
my pump, the mark would advance, but the diaphragm wouldn't hold the
vacuum.  It would not-so-slowly drop back to zero.  Is that right?

Any other thoughts would be appreciated.  I think this stuff is really
interesting.

Rob Hughes
'75 SII, 345, 727