Playing with a big block, chasing an off idle stumble. While checking the distributor, I noticed that the timing would retard as much as 8 degrees when I snapped the throttle. Made sure that the vacuum advance was disconnected to prevent false readings. Still the same result. Timing isn't erratic. In fact it's pretty solid while ramping up the rpm to full advance. Was just wondering if anyone ever saw a momentary timing retard during acceleration before.

Do you have a roller cam without the button to hold the cam in place?

Hydraulic cam. Street motor.

Take the distributor apart and make sure the advance mechanism isn't binding or missing parts.

Dial back light?

MSD will do that if the two wires are backwards the violet and orange wires
It will still start and run but as soon as you hit it timing will be all over the place and retard

Advance light. Guess that would be considered a dial back. Not using the advance feature. Never had a problem in all the years with it on my Cuda. Distributor is a Mallory Unilite, all self contained except for coil.

I asked because Tuner suggested eliminating that possibility first in a parallel thread about Mallory distributor timing on RFS
https://www.tapatalk.com/groups/racingfuelsystems/mallory-unilte-weird-timing-issue-t1763.html

Yeah. I thought I had another timing light home. I have to wait until tomorrow, when I can bring home my old school light.

Put an old timing light on it tonight. Timing was rock solid with no retard when snapping the throttle. Thanks guys.

Interesting. Thanks for posting the result. Always been slightly suspicious of it, and seen similar but not so severe just coming off idle.
I'll make sure to give it time stabalize or open the throttle slowly on future checks. Time for me to buy some timing tape and test against a regular light!

Where is your timing set?

With all electronic ignitions there is a certain amount of slew rate (delay rate)
The correct way is to curve the distributor to counteract the delay. Here's one of our videos showing the delay on our distributor machine.

https://m.facebook.com/story.php?story_fbid=1492409547544622&id=621247104660875

14 btdc @ idle. 34 btdc @ 2500.

Watched your video. Interesting. My problem was on a snap of the throttle. If I rolled into the throttle gently, the timing retard was not noticed. Like you said and was mentioned earlier, just the rate of the timing light relative to the actual timing events.

So what are you suggesting? The timing should be 5* more advanced than what you want when timing is locked out? My timing backs up 3* only by the looks of it when i steadily rev the engine to 4000. Using msd dist with an Ice Ignition box and locked out.

That's why I was suggesting the tach distributor in the other thread. In the worst case, it looks like a flat line. Obviously, Baldwincarbs may have similar setups. (I don't have FB, but could see the video)

The curve needs to be worked to counter act the delay.
Average is 1 degrees lose every 1,000 rpm past 1,000 rpm
So it starts at around 2,000 with 1 degree and by the time you get to 7,000 its 6 degrees.
Timing is based off of piston speed vs burn rate (chamber design) so taking a fast burn head such as a trick flow that wants 34 degrees at 7,000 rpm doesn't really want 34 at 4,000
We've seen 40 ft pound torque difference by applying a correct curve.

But wouldn't this only be necessary if you found the same delay with a standard timing light? Sounds like this timing loss would be something in the control unit, not in the distributor itself, but can be made up for in the distributor. Do different control units have different accuracies?
I remember the old days using an oscilloscope in a raster pattern and looking for an "S" pattern to determine timing chain stretch. Something else that is hard to see with just a timing light.

Is this a capcitive discharge/ multiple spark system?