My untimeable motor.

[DynaBro]

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]

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

 

[pnora]

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]

Timing chain cooked?

 

[eldubb440]

timing light have a dial on it?

 

[68-500]

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

 

[DynaBro]

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]

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

 

[MoparLeo]

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]

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.