My untimeable motor.

DynaBro · Thursday at 8:31 PM

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 · Thursday at 8:43 PM

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

pnora · Thursday at 8:49 PM

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 · Thursday at 8:55 PM

Timing chain cooked?

eldubb440 · Thursday at 8:57 PM

timing light have a dial on it?

68-500 · Thursday at 9:02 PM

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

DynaBro · Thursday at 9:45 PM

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 · Thursday at 10:20 PM

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

MoparLeo · Friday at 12:44 AM

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 · Friday at 1:28 AM

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 · Friday at 6:13 AM

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 · Friday at 6:52 AM

I had a bad bearing in my distributor.

Did the same thing as you are describing.

DynaBro · Friday at 10:15 AM

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 · Friday at 10:15 AM

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 · Friday at 10:20 AM

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 · Friday at 10:52 AM

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 · Friday at 12:14 PM

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 · Friday at 1:30 PM

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 · Friday at 1:45 PM

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.

DynaBro · Friday at 8:07 PM

Plugging PVC port did nothing. It is sucking air. Installed a brand new grommet and it's just as useless as the old one. Is there anything I can wrap the valve in to make this stupid thing tight? The slightest breeze will blow it out of the valve cover.

What happened this round: I decided to also monkey with the carb idle screw to attempt balancing the timing and idle. This gets VERY frustrating.

With timing set 10ish retarded I will back the idle screw out 1/8 turn. That's all. Just the tiniest adjustment. Rev it so the mechanism can settle. Once it settles this causes the timing to slowly advance until past TDC and bog out. Just a tiny little twist.

I will put it back, but this causes the timing to retard beyond the 10ish BTDC to closer to 20-25 BTDC after it settles. Massive swings with the slightest idle screw adjustments. It does not return to the previous timing/idle setting. It. Will. Not. Balance.

I did this over and over and over with idle, timing, every conceivable combination. It retards, it advances, it refuses to be content.

Would someone please confirm timing marks on this photo? 10 before is the short line next to the 10, correct? So correct timing lies between that line and the long one at the bottom?

My untimeable motor.

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