Erratic Timing

AJ/FormS said
After you shorten the slots to say 22 degrees, and run an initial of say 12* for a total of 34*, then that long looper will no longer top out at the same Rpm as before.

Mattax said
I'd set the initial timing at whatever it needs to be for your car. Then go from there. Setting it at 2600 to 3000 is for hot rod and racing setups.
If its not stable at the idle speed, try increasing the primary spring's initial tension. That's done by rotating the spring perch on the cam plate.
If you need weights in better condition, ask halifaxhops.

OK so sounds like I shouldn't run the advance as is. I need to set initial at idle, then (if necessary) shorten the slots to make the mechanical advance match. Only once that's done can I fiddle with the springs to get the right curve. I think I've been getting ahead of myself!

Mattax said
For example, acceptable timing range for '68 using 5* initial (per Plymouth FSM)
View attachment 1715306919

CAP and CAS 318's at least through '69 have the initial timing spec'd at either TDC or 5* ATC.
From 1400 rpm to 4600 rpm the timing very similar to the non-smogged 318 shown above.

This seems similar to what's in my 1972 service manual. I think my engine is 77 (the number just might be 71?) with electronic ignition, not lean burn.
Screen Shot 2019-03-21 at 11.36.29 PM.png

Screen Shot 2019-03-21 at 11.36.29 PM.png

My advance is 15, right in the middle, so those degrees would be 3*, 9.5*, and 15*, if I'm guessing right. Since I can't idle below 1100, and my timing light shows 1* at 1100, then these numbers would match what I'm seeing, meaning that my initial timing is 5* retarded. Yikes.

67Dart273 said
Also from long ago, I think Crackedback posted this. Here's a chart showing approximate advance re: slot length. Also, are you aware of the aftermarket FBO advance limiter plate? Some guys have used these and say they work OK
How to limit mechanical advance in a mopar distributor, tuning for street, strip or all out racing, cure that rich stinky idle, win races
=======================================================
Dimensions for Mopar distributor slots, in DISTRIBUTOR degrees

Modifying advance slots
degrees / slot size
6.............. .340
7................355
8................375
9................390
10...............405
11.5 ...........420
12...............435
13...............445
14...............460
15...............475
16...............490
17...............505
18...............520

Thanks, this is just what I was looking for! I am debating getting that plate, but it might just be too easy for me... lol

JoeSBP said
I don't think I have ever owned a carbed engine that would hold timing rock solid at idle, always bumps +/- a degree or two

Good to know this is normal. Thanks!