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1 11th January 22:41
External User
Posts: 1
Default big block ignition timing

Hey wondering if anyone can help me. I have a duster with a 400 big block
and I am having some trouble getting the timing right. It has an
aftermarket cam (I don't know the specs since it was installed by the
previous owner), and the initial timing right now is set at about 48
degrees before top dead center. That seems way off to me since total
timing should only be about 36 degrees, but when I put initial timing back
to 15 degrees (to allow for the distributor's mechanical advance) it
backfires and won't hardly run. At the current timing the idle is very
rough to the point where the car visibly rocks and sometimes stalls when I
put it in gear. It has all kinds of top end power, however, and when I
retard the timing at all, it falls flat about halfway through the power
band but the idle smooths out. What's going on? Is the idle supposed to be
rough because of the big cam, or is there something else going on? I also
have no vac*** advance on my distributor. Not sure if that affects it at
all. Any advice would be appreciated!
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2 11th January 22:41
External User
Posts: 1
Default big block ignition timing

big cams can be tricky especially if your running an automatic. my DC cam I
put in my 440 was a pain for a while. yeah 48 is a lot. does sound like cam
is advanced . some questions to look at are:

has anyone messed with the advance weights or springs,

(dumb question here but worth asking because I've seen it done by accident)
are the plug wires possibly off by one hole on the cap?

is there any vacuum leaks around the carb or manifold, I check it with
engine running and spraying around intake with carb cleaner...use the little
straw to control the spray.

what manifold are you running? mine acted like yours and I am running the
factory manifold. mine needs a good single plane performance intake.

is there an adjustable timing chain set on it?

what torque convertor you running?

have you seen the brand name or part number on the cam? if so you can call
the manufacturer of the cam for info.

those are just some things that come to mind here early in the morning. let
me know and I know others here and over in alt.hi-po.mopars can help more.
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3 11th January 22:41
External User
Posts: 1
Default big block ignition timing

Something is not right so you have to eliminate a few things.
1. you need to check you timing order 18436572 easy enough to mix up
some times especially 5 & 7.
(No. 1 is drivers side front!) (distributor turns counter
I will try to mention everything cause you would not be the first
to think as some cars are pass front is no 1 or that as on chev or
mopar small blocks with distributor going clockwise .

2. Now you need to physically check that your 0 mark on the Harmonic
balancer actually lines up when N0.1 is at top dead center
you can first bring it up and see if it's close using a pencil in the
spark plug hole but it's not true accurate! What you need to do is you
will need a piston stop.
padMOPAR - TDC Indicator Tool
I make mine by knocking all the porcelain and guts out of a spark plug
.. taping it out with 5/16" tap. I take a longer 5/16" bolt and cut
threads up to head of bolt and round end. put on a nut to work as
locking nut and thread through old spark plug and you have an
adjustable piston stop / TDC tool! (I dipped mine in plastic tool
coating on the end after assembly)
Now near the top of compression stroke (20 to 30 deg from physical TDC)
install tool turn in and move engine till it gets a positive stop.
(lock 5/16 bolt in place so it's the same depth when you put it in
later) Accurately measure distance from 0 mark on timing cover to 0 on
harmonic. (also mark balancer at 0 timing mark with a magic marker)
now back engine off turn tool out move motor past TDC a little more
than needed. now screw your tool in and back engine up till it again
stops . This tool has made the engine stop at exactly the same spot
before and after TDC. now measure distance from 0 mark on timing
cover to 0 on harmonic . (again mark with marker) It should be the
same lets say .500. it should have stopped engine exactly the same
amount before and after the timing mark. Recheck if your not sure "if
it's not right" 1/2 between your magic marker marks is true TDC. If
your out you need to replace balancer the ring as moved!!

3. . What type of dial back you got. buy timing tape P4529070AB
its a few bucks and installs left to right from timing mark
can be bought at your local speed shop or mopar dealer plus ??

a single non dial back timing light is often is the best using timing
tape as the dial backs can sometimes be way out of whack!!!

4. Are the weights in the distributor allowing it to advance?? Are
there even advance weights in it?? it may be a non advancing
distributor (you said there was no advance on it??????) has vacuum been
removed (cool) or not used (cool)
pull cap and look grab the rotor and it should be able to move 15 or
so degree's counter clockwise (advance).

The distributor should give 15 to 25 extra deg of timing all in
anywhere from 1500 to 3500 depending on the springs in the
distributor! 36 to 38 should be optimum!

Give us some more feed back!
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4 11th January 22:42
External User
Posts: 1
Default big block ignition timing

It does not have one of thes conversion blocks to alllow for a 440
distrubutor in a 383/400 does it??
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5 11th January 22:42
External User
Posts: 1
Default big block ignition timing

I am running a 727 torqueflite auto, I believe the torque converter is a
factory item, it feels awfully tight at idle (maybe part of the reason it
stalls with the timing advance?). Also running the factory dual plane
intake for now. I had a problem with the 5 & 7 spark plug wires being
mixed up when I first got it, and anytime I laid the pedal down it would
backfire and belch flame out the carb. I switched them back and that fixed
the problem. All the other wires seem to be going to the correct plugs. It
runs pretty good with the timing advaced like it is now, with the
exception of the really lopey idle. I have not checked the advance weights
in the distributor but i'm planning on it. Also, i never thought of
checking the alignment of the timing cover with the balancer at TDC, but
I'll have to do that too. Thanks! Also, if indeed I do have a big long
duration cam, should the idle lope go away with less ignition timing
advance? This is my first project car and it's definitely a learning
experience. I appreciate everyone's advice!
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6 11th January 22:42
External User
Posts: 1
Default big block ignition timing

Are you certain the cam timing relative to the crankshaft is correct to begin
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7 11th January 22:42
External User
Posts: 1
Default big block ignition timing

Generaly the idle with big cams is better with more advance! I run a
locked out distributor at 39 deg so it is at 39 from idle to 7200??
The reason being idle quality and better bottom end. Do have a 10 deg
retard to help get it started!
There is something amiss with your car I would have thought someone
installed a small block distributor and it was retarding insted of
advancing as RPMs come up ( small block distributors are the same
dimensions as a RB 413/426/440) but since yours is a 400 only a
400/383 distributor will fit without the spacer block???

like I said just in case take cap of and turn roter CC if it moves that
way against advance springs it's right. If it won't but moves aginst
the springs clockwise it's wrong rotation and is retarding as it revs
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8 12th January 01:19
External User
Posts: 1
Default big block ignition timing

Had a moment this morning, and I took the cap off and tried to turn the
rotor. It did not seem to turn at all one way or the other! Is there such
a thing as a distributor with no mechanical advance? I also found a manual
on 70s and 80s rear drive chrysler cars at Autozone on my way to class and
I haven't been back to the garage to double check, but seems like the
wires were rotated one space clockwise from where they are in the diagram
in the manual. If this were the case, would it even run?
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9 12th January 01:19
External User
Posts: 1
Default big block ignition timing

yeah but very crappy. the main thing is to rotate the crank to number 1 TDC
and check the rotor to make sure its aligned with number 1 plug wire or
close to it, and not another cyl.
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10 12th January 01:20
External User
Posts: 1
Default big block ignition timing

Checked the distributor again when I was over there installing the new
battery & alternator and all the wires are in the right place and going to
the right plugs and the rotor is at the number one terminal at TDC. Here's
the weird part: the old alternator had spots for two wires to hook up on
the back; the one that's held on by a nut and one that slides onto a flat
terminal. The new alternator had three wire hookups on it, so I looked
around at the wiring and found that along with the two wires that were
attached to the old alternator, there was a third wire that had been
wrapped in electrical tape and was hanging off to the side. Upon
unwrapping it, I found that it has a plug that fit perfectly to the third
terminal on the new alternator. When I plugged it in and started the car
again, the previously lopey idle had smoothed out. I have no idea what is
going on and have not yet had a chance to trace this "mistery wire." Is it
possible the wire goes to some kind of electronic advance/retard mechanism?
Am I just losing my mind?
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