Slant 6 engine ignition timing stays retarded.

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dodgemahal

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I'm tuning the slant in my 1973 Dart. I did all the usual stuff---- plugged the distributor vacuum hose after disconnecting. Set idle at 750 rpm. Adjusted mixture to highest vacuum @ 18" with a rock steady needle.
With the distributor rotated all the way counter-clockwise (confined by the slot), the best I can get is 5 degrees ATDC. It runs like a turd. With the vacuum advance reconnected it runs much better of course, but I can tell something isn't quite right. I've been racking my brains for days but can't solve this. I considered lenghtening the slot. I figured it's time to ask the guys who know way more than I do. Thank you.
 
dodgemahal said:
the best I can get is 5 degrees
Click to expand...
5 deg Atdc is retarded, you want to have it 0 to 5 to 10 Btdc so it's advanced. If you are trying to set it per factory spec (67 dart 273 with CAP calls for 5 Atdc) it will probably run like a turd.

0 = 5 advanced over factory
5 = 10 advanced over factory

I typically run 0 to 5 advanced as the CAP dist has a very aggressive advance curve in the lower RPM and vacuum range.

It is about the same as the non CAP after about 1500 to 2000 rpm
 
Dana67Dart said:
5 deg Atdc is retarded, you want to have it 0 to 5 to 10 Btdc so it's advanced. If you are trying to set it per factory spec (67 dart 273 with CAP calls for 5 Atdc) it will probably run like a turd.

0 = 5 advanced over factory
5 = 10 advanced over factory

I typically run 0 to 5 advanced as the CAP dist has a very aggressive advance curve in the lower RPM and vacuum range.

It is about the same as the non CAP after about 1500 to 2000 rpm
Click to expand...
I did not explain this very well. Your first paragraph is exactly what I'm looking for. I want 3-5 degrees advanced(BTDC) to begin with. I may modify that later. Factory spec happens to be 0 degrees. The problem is I can't advance the timing past 5 degrees retarded(ATDC) even rotating the distributor as far as it will go. Oh, I can retard it to infinity if I want. That's the issue.
What does CAP mean? Clean air something? How do I know? It did come with OSAC, but I disconnected that.
 
What is preventing you from rotating the dist?

You should have enough clearance to rotate it 15 deg in either direction
 
Dana67Dart said:
What is preventing you from rotating the dist?

You should have enough clearance to rotate it 15 deg in either direction
Click to expand...
Because the screw that fastens the distributor down is confined in a metal slot. I've got it as far as it will go. As I said in my original post, I was thinking about lengthening the slot so I can go further. Would you like a picture?
What is CAP?
 
Might have to pull the distribtor and rotate it one tooth. Also, there is a second adjustment slot on the back side of the distribtor.
 
dodgemahal said:
As I said in my original post, I was thinking about lengthening the slot so I can go further. Would you like a picture?
What is CAP
Click to expand...
Yes please post photos.

CAP is Cleaner Air Package. It was Chryslers attempt to add emissions controls to their engines
 
I have tried clocking the distributor by one tooth already. That gets it way, way off the mark. Good idea though.
 
Is the plastic driven gear on the bottom of the distributor worn out? Pretty common on /6s with a lot of miles on them.
 
SIX225 said:
Might have to pull the distribtor and rotate it one tooth. Also, there is a second adjustment slot on the back side of the distribtor.
Click to expand...
I'll look for that second slot though I can't imagine what it would look like. Can you be more specific? I've had this dist out many times in the last several months and don't remember seeing something like that.
 
dodgemahal said:
I'll look for that second slot though I can't imagine what it would look like. Can you be more specific? I've had this dist out many times in the last several months and don't remember seeing something like that.
Click to expand...
Turn distributor upside down so the drive pinion is pointing toward you. Notice how the distributor hold-down plate is held to the underside of the distributor body with a bolt. Notice how that bolt goes through a slot rather than a round hole. There you are.

Also, if you're getting significant vacuum advance at idle, your settings aren't where they should be, but that will likely self-correct once the base ignition timing is where it should be; because it is too retarded, you will have had to open the throttle wider to achieve the 750 rpm idle speed, which will have uncovered the vacuum advance port.

Spec in '73 is TDC, but you'll have a much better-running car, without creating new problems, if you'll use the 1960s spec of 2.5° BTDC. Even better still if you will bypass the OSAC valve (right side of firewall on the engine side) and just run the hose directly from the carburetor to the distributor.

Also-also, make sure both of the distributor's O-rings are present and in good condition; info here.

Also-also-also, tune-up parts and technique suggestions are in this post and Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download.
 
You can see the screw is pegged against the end of the slot. The other end is jammed against the block. Read: NO wiggle room. I'm glad to know there's another adjustment point. Great info Dan!
20240920_163740.jpg
 
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