[AMC-List] optimum AMC six ignition timing

[Tom Jennings <tomj@xxxxxxx>]

I'm still working on determining the right timing advance curve
for the 258. I can tell you so far that what works for the AMC
V8's does not work on my 258 six.

The V8 rule of thumb is "36 - 38 degrees of ignition advance
timing, all in by 2500 - 3000 rpm" which usually translates
to softer centrifugal springs and an initial setting of 10  -
12 degrees. Done!

I was wrong; too much advance for the six.  (John Elle, you are
vindicated.) It definitely wants more advance than the factory
settings, but the curve is a lot flatter (later).

The V8 curve on the 6 pings too much at low/midrange (2000 - 2500
rpm) and retard-backfires above 3000 rpm. In the low/midrange
RPM, it's very temperature sensitive; this might actually be
good, in a sense, if it means I am on the hairy edge of too much
(so now I know what it wants in that range).


I used a Mr. Gasket spring kit for Ford (Duraspark). These
are far too soft (too early too fast)! Full advance was around
2700. I had a couple of old Duraspark distribs and pulled the
springs from them. None are marked, so I graded them by how
far each deflected under a random mass.

I just stuck in stiffer springs, now it's all in by 3200. I'll
try that for a while, but I think it's still all in too early.

Wouldn't it be funny if I end up with factory springs. Very
funny.



After 500 miles, the RN9Y plugs look just fine; it had RN12LY's
in there.  (Champion.) The 9's are the next-coldest plug
available; there is no 11 or 10. There's almost no difference
between the 9's and 12's in color. Weird.

But moving from RN12LYC to RN9Y did not affect pinging enough
to measure. After changing the plugs, I did road-setting of
static advance, and when I was done, I ended up with the same
static advance (10 degrees) as with the RN12LY's!

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