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 vaccum advance on my distributor. Not sure if that affects it at all. Any advice would be appreciated!
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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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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 clockwise!!!!!!!) 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 pad pad MOP-P4349737pad$22.95 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 ?? http://www.manciniracing.com / http://summitracing.com/index.htm http://www.jegs.com /
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! Barry
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It does not have one of thes conversion blocks to alllow for a 440 distrubutor in a 383/400 does it?? Barry
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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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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??? Barry
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 up!!!!
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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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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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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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do you have an aftermarket ignition system?

mechanism?
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Yea the electronic lean burns had no advance (it was done by the computer) you need a different one. Thats why there is no advance canister!! If you set enitial at 36 to 38 it should run great but it may kick back on the starter to start! I run mine locked at 39 but I have a 10deg msd start retard. Barry
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well that would explain a lot. yeah go MSD or Mallory

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Yeah, you're right. I took it apart this morning (probably should have done that to begin with) after finding a small arrow I overlooked earlier on the reluctor pointing clockwise. The manual I have shows the big block distributors rotating counterclockwise and small block distributors rotating clockwise so I figured it was the wrong one and took it apart to check the advance weight assembly. There is not one. This engine is not equipped with lean burn or any other emissions control systems, so I am guessing the previous owner stuck a small block lean burn distributor on it. Definitely going with a new distributor. Thank you everyone for all the advice!!!!!
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wrote:

Are you certain the cam timing relative to the crankshaft is correct to begin with?
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Is this a street car or race car??? If it is street find a distributor with vacuum advance unit run about 15 degrees initial 20 in the dist-as a starting point. Hook the vacuum advance to ported source not full time.. The vacuum advance us needed in the cruse mode to advance the timing for fuel economy.. Initial & dist & vaccum advance total about 50-52 degrees. Make sure the mechanical advance does't come in too soon if it does the idle will be unstable. How much vacuum does it have at idle ?? Do you know what the compression is ?
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The short block is stock with 8.2:1 compression, the ignition is an ancient GP Sorenson unit with a vaccum advance-less distributor(not sure if it is a factory piece or aftermarket). It is basically a street car with a cam (for now). I amd looking at an MSD ignition and distributor for it to replace the GP Sorenson unit.
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Well just set the timming for now at 37 total and it should run fine. may be a little touchy to start but if you were getting it going at 45 LOL!!!! With that low of compression they will not ping but 37 will make it run best! Barry
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Recieved and installed my new mopar performance distributor the other day along with some new plugs and wires, and the car now runs better than my '94 ram, and I haven't even had a chance to put a light on it and fine tune the timing yet! Thank you everyone for your help!
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most excellent!

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