Re: IML: '73 LeBaron Spark Knock at Part Throttle

[David Whitney <david.whitney@xxxxxxxxxxxx>]

Hi, Jay --

Having just gone through a similar experience with the 440 on a lesser
Chrysler (but not much lesser), I think vacuum is a good place to start.

Initial advance can be tricky -- I discovered that my engine had the CAP,
which meant initial advance was 5 AFTER, not 10 BEFORE.  That made a lot of
difference.  I set it by ear, and it was at 10 before so I congratulated
myself on a fine job.  Then I tried to take it on the freeway and it
sounded like I was popping popcorn in the engine compartment.  Back to the
book and lo and behold, 10 before was wrong.  So I got out the spiffy
timing light, set it to 5 after (lined up with the conveniently placed
round hole in the plate).  Back to the extremely short onramp at WOT, I
shifted from second to third at 65 with nary a ping.  Beemers and Volvos
scrambled to get out of the way because they don't like to see anything
that big that drives like they do.

The advance controlled by the vacuum line to the diaphragm on the
distributor is adjustable with an allen wrench -- you can dial in fully
advanced at idle up to a 15 degree curve.  You may want to adjust that
curve.  If you are running a high performance engine, you may want to
upgrade to the Mopar race distributor.

To test the ignition system for electrical isolation at idle, mist the
engine with water from a spray bottle.  If you see the aurora borealis
under the hood, you know what to do.  If you're worried about pulling the
engine off the motor mounts under acceleration, you can install a torque
chain.

Those carbs require about 15 adjustments before you are ready to start
adjusting the timing.  The later Carters really got a bad rap because they
are not as easy to work with as the AFBs, but as performance carburetors
they are among the best because they are so tuneable (is that a word?).

Now to the actual stick-my-neck-out diagnosis -- Assuming that vacuum is
not leaky and carb is set to spec and advance is properly adjusted and
electrical is isolated, I have one question:  how's your timing chain
doing?

Enjoy,

David








I seem to recall some discussion recently on the list about 440s and spark
knock (pinging) at part throttle. I noticed this week that my '73 Lebaron
seems to be exhibiting just that symptom, but only when there are more than
two people in the car. There are some acceleration issues that should be
cleared up with some vacuum line replacements this weekend when my son and
I put a new power brake booster on the car, but the pinging at part
throttle (not WOT) worries me. For those willing to attempt long-distance
diagnosis, the motor has less than 50,000 miles and came from the factory
with the HP cam. I have replaced the ThermoQuad with an Edelbrock Performer
1406 (wow! what a difference!) Did the discussion I seem to be remembering
center around deteriorated motor mounts and the #8 spark plug grounding
against the subframe under certain acceleration conditions?

Thanks in advance for any and all help!

On another topic: I may have the chance to buy a '76 NYB four door hardtop
(the year of my high school graduation!) I know very little about the car
except that it looks pretty good and supposedly has been sitting because of
a bad fuel pump. Anything I should look for/look out for on this car? I'd
like to have it, but I'm not looking for a major project right now
(actually I am, but it will probably be a '72 Dart Demon my son thinks he
can't live without. Well, at least it's a Mopar . . .)

Thanks to all!

Jay

Jay King
Meridian, Mississippi
<a href=mailto:j_king@xxxxxxxxx>j_king@xxxxxxxxx</a>

Honey Gold 1973 LeBaron 4DHT
--
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