My untimeable motor.

DynaBro · 2025-09-04T20:31:15-0500

1970 383. New Edelbrock AVS2. New plugs. New V Belt. New Distributor cap and rotor (magnetic internals). MSD 6A ignition. Good connections at both valve cover ports. Vacuum advance is plugged into the 3/16” TIMED VACUUM (Distributor vacuum advance port for emissions controlled engines), NOT the 3/16” MANIFOLD VACUUM (Distributor vacuum advance port for non-emissions controlled engines) port.

I cannot get this thing to hold timing. Some of you have suggested possible issues in a thread about another topic (like the secondary vacuum flaps sticking) but I'm at the point it was necessary to start a dedicated one because I am so many hours into this mystery that I'm out of ideas.

So, I set timing with vacuum advance plugged off per instruction using a classic strobe. Distributor slipping is not the cause per the paint mark test. I rev engine. I check again. Timing is significantly advanced or retarded. Like over 10 degrees. I play with the carb a bit to make sure everything has calmed down to idle and nothing is sticking. No change. I juggle the balancer, seems tight. Sometimes when it advances the idle does not! Sometimes it does. It's not reliable in any way, sometimes the timing change is retarded, sometimes advances, and always by like 20 degrees.

Out of ideas here. Please help.

Don Frelier · 2025-09-04T20:43:32-0500

See if the centrifugal advance plate is sticking.
I've seen it happen.

pnora · 2025-09-04T20:49:47-0500

Timing for the most part is all distributor related and its mechanical functions. Leave the vacuum can plugged off and go from there. .

66 Sat · 2025-09-04T20:55:58-0500

Timing chain cooked?

eldubb440 · 2025-09-04T20:57:53-0500

timing light have a dial on it?

68-500 · 2025-09-04T21:02:13-0500

Also check that the VA bits are properly secured mine was missing a screw and acted similarly.

DynaBro · 2025-09-04T21:45:39-0500

no idea what I’m doing inside a distributor cap. I poked around and adjusted the magnet by accident and then car wouldn’t start. Luckily I figured out what I’d done but I don’t know what’s what in there.

No strobe does not have a timing light.

Cop car wagon · 2025-09-04T22:20:16-0500

Your throttle plates are open past the transfer slot.
You cannot maintain an idle, therefore you cannot set timing

MoparLeo · 2025-09-05T00:44:00-0500

Swap distributors. Sounds like mechanical problem.
You never specified what distributor was in it.
Was this a running driving car before ?
New problem ?
More details.

Geoff 2 · 2025-09-05T01:28:36-0500

When you rev the engine after setting timing....does the engine come back to the same idle rpm?
If yes: sounds like the centri weights in the dist are sticking
If no: higher rpm, sounds like weights could be advancing with the rpm.

Disconnect & plug the PCV port. Try again, report back.

1967coronet · 2025-09-05T06:13:07-0500

DynaBro said:
no idea what I’m doing inside a distributor cap. I poked around and adjusted the magnet by accident and then car wouldn’t start. Luckily I figured out what I’d done but I don’t know what’s what in there.

No strobe does not have a timing light.

Sorry but I have to ask...
How do you know the timing is moving 10 degrees without a timing light ?

YY1 · 2025-09-05T06:52:14-0500

I had a bad bearing in my distributor.

Did the same thing as you are describing.

DynaBro · 2025-09-05T10:15:11-0500

1967coronet said:
Sorry but I have to ask...
How do you know the timing is moving 10 degrees without a timing light ?

Typo. Very frustrating evening. I meant the light does not have a dial.

DynaBro · 2025-09-05T10:15:47-0500

YY1 said:
I had a bad bearing in my distributor.

Did the same thing as you are describing.

I am leaning heavily toward just replacing the distributor.

DynaBro · 2025-09-05T10:20:35-0500

Geoff 2 said:
When you rev the engine after setting timing....does the engine come back to the same idle rpm?
If yes: sounds like the centri weights in the dist are sticking
If no: higher rpm, sounds like weights could be advancing with the rpm.

Disconnect & plug the PCV port. Try again, report back.

Very interesting theory. I will do this this afternoon.

MoparLeo said:
Swap distributors. Sounds like mechanical problem.
You never specified what distributor was in it.
Was this a running driving car before ?
New problem ?
More details.

It's a typical MOPAR Performance. It had Blue Streak cap and rotor that I replaced with newer stuff. I'm not even certain it's a "new" problem as the car has run but never quite right and I just finally got the tach working to verify RPM. It has always had some finicky issues, one of which is this low thrum thrum thrum sound at cruising speeds which I am not sure is timing issue or the Air Grabber being open. (I have to make sure it's physically closed because the previous owner removed the cable and covered the grommet hole with the ignition box).

threewood · 2025-09-05T10:52:12-0500

Cop car wagon said:
Your throttle plates are open past the transfer slot.
You cannot maintain an idle, therefore you cannot set timing

And if that's the case, he is going to need more timing advance to be able to adjust the curb idle/throttle plates.

Fran Blacker · 2025-09-05T12:14:02-0500

They problems with some MP distributors said Mopar Action E Booger. Check distributor for side play. That will let timing bounce around.

68 Sport Satellite · 2025-09-05T13:30:33-0500

Fran Blacker said:
They problems with some MP distributors said Mopar Action E Booger. Check distributor for side play. That will let timing bounce around.

I remember reading that. He even suggested a bushing with a set screw to combat this which seemed to work.

DynaBro · 2025-09-05T13:45:20-0500

Well broke down and I ordered a new one from Rick but in the meantime will keep trying any of your ideas that aren't super work intensive to try and nail it down.

My untimeable motor.

DynaBro

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