Chuck,
Advancing past a certain point won't actually do any good.
That point is called MBT (Mean Best Torque (unless my
notoriously porous brain dropped something)), and anything
beyond that will just increase your problems (as Jeff Z said)..
Having said that, the '72 is a hard puppy to get to ping,
since they lowered the compression to 8.0:0 (for the US)
for emissions-related reasons (meaning I really don't know).
My guess is that they wanted to increase the advance for
more complete combustion..
My technique is to leave the vacuum advance connected,
and advance the timing until it sounds like too much (starts
to stumble a little), the back it off a bit past the
ideal (fastest smooth idle) point, then a touch more for
safety. and listen carefully for knocking. This is a crude
and indefensible method of setting the timing, but it's
always worked for me (with apologies to H.S. Thompson, and
real mechanics, and my mother (sorry, mom)).
Looking at my trusty (and usually trustworthy) Haynes manual,
I see that they indeed made the advance curve steeper for
the emission control models (although I think there's a
misprint here, as 2 advance levels (19 and 23 degrees) are
labeled "2,300 to 2,500 rpm".
In any case, it's difficult to figure out what they're saying
here, but it looks to me like it wants more than 10 degrees
at idle. Big news, that. Looks to me like it might want
as much as 26 degrees at idle, depending on what the hell
that "19' at 2,300 to 2,500" line is supposed to be. You
might try timing it statically, and see how much (centrifugal)
advance you're actually getting at idle. The centrifugal
advance comes in at 500 RPM on emissions distributors.
I'd never heard of a timing light with an advance dial, as
Jeff Z. just described. Woo hoo! Gotta get me one of those!
As Jeff said, the best way to set the timing (from a
performance standpoint) is to set the correct total (full
advance) timing, and Jeff's light sounds like the easiest way
to do that (you can also guess and/or mark off the total advance
on the timing cover, but that's a crude hack (cough)).
However you do it, you should rev up the engine after
setting the timing, and see that the timing mark moves to
somewhere in the vicinity ofthe total advance figure
It looks to me like your engine ('72 emissions) wants
37 degrees total advance (7' static + 30' advance at ?? RPM)
Enough nattering on. Good luck with it.
-Hans "advanced *way* beyond MBT" Huber
P.S. Does anybody have a newer revision of the Haynes
manual that has the correct info on centrifugal advance
for emissions dizzys? My Haynes is old enough to be missing
the title page (and at least pages 111-116), and is nicely
rebound with black duct tape, so I don't even know when it
was printed.
On Wed, 29 Jul 1998 08:24:19 EDT Chuck Ciaffone wrote:
> It happens every time I tune my '72. I set the timing,
> using a timing lite, to about 10 degrees advance with
> the vacuum advance disconnected and plugged. It runs OK.
> Then I start turning the dizzy for more advance, and it
> runs better. SoI would guess that I probably run normally
> with about 15 or so degrees of advance, AND it still
> never seems to ping. Can/should I just keep advancing
> the timing till it pings? What's probably going
> on here?
>
> chuck
> --
> =====================================================
>
> chuck ciaffone chuckc@ibm.net
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