Re: [ihc] Dialing it back(Pi?...no, spark!)

["Ryan Moore" <baradium@xxxxxxxxxxx>]

----- Original Message ----- 
From: "Jim Grammer" <jgrammer@domain.elided>
To: <ihc@domain.elided>
Sent: Wednesday, June 09, 2004 13:41
Subject: [ihc] Dialing it back(Pi?...no, spark!)


<snip>
>
> Of particular interest is the 'cut-in' point of the vac advance, and how
> quickly the advance comes in above that point. There seems to be a fairly
> wide range of characteristics among the 'stock' type advance units. The
> cut-in point that's often stamped on the pull bar may or may not be
accurate
> either. On top of that, older trucks like ours are often victims of wrong
> parts swapping(looks the same, fits, must be right, right?).
>
> Case in point, '73 T-all 392 - towing in hills, a nice comfortable cruise
is
> about 50MPH in 2nd gear. 3300-ish RPM, so the mechanical advance is
> 'all-in'. Manifold vacuum wants to be around 6-8", depending on the grade.
> The cut-in point of the vac advance on the truck when I got it was right
> about 6". So you're climbing, and can't stay in that 50MPH sweet spot
> without the vac advance coming in. Hello, ping :( Sure, you could back off
> the static timing or pull back the max. mechanical advance, but the
truck's
> running great and making *real* good power at that RPM/load :). I found a
> vac advance unit in my collection that doesn't cut in until 8" of vacuum.
> Problem solved, mostly. I will still need to limit total advance if I want
> to tow with 87 octane, or run the leaner metering rods in the AFB even
with
> 89 or 92 octane.
>
> I can't see any reason to bring the vac advance in on an SV below 8-10" of
> vacuum, YMMV. All this makes an excellent case for following Greg's lead
and
> swapping to Delco dizzys, for which you can readily buy mechanical advance
> curving kits and adjustable vac advance cans.


I changed the vac advance can on my scout a while ago... when I needed a new
one, went to one with a slightly higher amount of advance but also a higher
amount of vacuum to activate.  Works great, I went to manifold vacuum now
for the vacuum advance the other day, and I'm really happy with the results.
Gave me more usable power throughout the rpm band via the change I was able
to make to the initial timing and how it effectively retards it under load.
One of the things I was having issue was that in low cruise I wasn't getting
much vacuum advance with ported vacuum due to the low RPMs... that meant
that if I advanced it to most effective at cruise I was pinging on regular
under load, but no ping under load wasn't my best power at cruise... all
better now though....

If I could just track down these other problems that waste gas (the
electrical stuff) it'd make life a lot easier and I think would help my fuel
economy a good deal.  Just going to manifold vacuum has given me a few extra
MPG over what I was able to attain previously).

On that note (hijacking the thread to a degree), I still can't figure out
what my problem is.  The next time it happens, would it be safe to unplug
the alternator as a way of checking to see if it is the problem?   I don't
really think it is (don't understand how charging to the battery could cause
the engine to lose power in the way it does), but I want to try to cover all
options.  Once I go to GA at the end of the month, I can't bring the scout
back to TN until I have the problem identified and repaired.

> Another tip on making timing marks visible. Both the damper mark and the
> timing scale cast into the front cover are most easily cleaned from
*under*
> the truck. Slather a rag with solvent and do the scale by Braille. Go get
> one of the new-fangled touch-up paint applicators in your favorite bright
> color. They have a ball point applicator as well as a brush. The ball
point
> is just the ticket for your freshly cleaned damper groove, and if you
prime
> the tip a bit it'll write upside down long enough to mark the damper from
> the bottom. If your arm's skinny enough you can use the brush to highlite
> the marks on the timing scale.
>
> Jim
>

I used a whiteout pen thing to make the timing mark visible, worked really
well and I can still see the mark clearly... I can kinda read the scale...

Thanks,
Ryan


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