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Discussion Starter #41
Dave, that’s an email address. Not sure I follow your “package” recommendation?
 

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See that number at about the 7:00 o'clock position, it is a ZERO, 0, LEAVE IT THERE, DO NOT CHANGE IT. Mark the dampener.

You would have that info already if you had sent me your email request for the "vacuum advance stop plate information package" as I outlined.

It has how to do it procedures, and even pictures, so anyone can understand it.


Thank you for the picture of the dial, it will be included in the package, with a capitals "DO NOT USE THE DIAL BACK FEATURE ON ANALOG SYSTEMS".
 

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Discussion Starter #44
See that number at about the 7:00 o'clock position, it is a ZERO, 0, LEAVE IT THERE, DO NOT CHANGE IT. Mark the dampener.

You would have that info already if you had sent me your email request for the "vacuum advance stop plate information package" as I outlined.

It has how to do it procedures, and even pictures, so anyone can understand it.


Thank you for the picture of the dial, it will be included in the package, with a capitals "DO NOT USE THE DIAL BACK FEATURE ON ANALOG SYSTEMS".
Just sent you an email
 

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Discussion Starter #46
Yes Dave. Now I have a lot of reading to do. Thank you for all the information
 
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Discussion Starter #47
Had some time to troubleshoot today.
1. Intake bolts were a little loose. Retorqued to 35ft-lbs
2. Timing was at 5 deg without vac. Adjusted to 9 deg without vac. With vac, it went to approx 18deg. All done with my timing light set to zero degrees.
3. Also retorqued starter bolts were a bit loose

Took for test spin, felt like it ran better. Pretty hot day here, Intake coolant temperature was 195deg, but did burp some coolant from rad after I pulled in garage. It’s never done that, but it’s hot today.

Start up after sitting, cranks strong without kick back, but RPMs do fluctuate A little at idle (like 50rpm) after start up but I think that may be normal due to cam?

Looked at distributor and I do not have the small vacuum tubing stop on the vacuum advance outlined in Dave’s detailed procedures.
 

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And this is not good to use?
I've been using this same timing light for over 40 years, it works fine no matter where I set it. I've checked it at 0 and at 20, its dead nuts accurate.
 
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NOPE, IT AIN"T, NEVER WILL BE ON AN ANALOG IGNITION SYSTEM. ONLY time the dial back is accurate is on an EFI setup where the EFI computer sets the timing curves, that is what dial back is designed to do, that is all it does, NOT ANALOG compatible.

Now, I think I would try 12 to 12 initial degrees, and with the 9 degrees the vacuum advance gives, connected to full manifold vacuum, the IDLE timing should go to 21 to 23 degrees, right in the ball park.

One test, timing light connected and dial back off, vacuum advance hose disconnected and plugged, engine idling, is the timing light solid no movement, no added timing to idle, back and forth, or, does the timing fluctuate up and down??? If the timing fluctuates, if you have one, try a heavier spring on the mechanical advance and see if the fluctuation either gets less, or stops, and the timing stays steady at idle.

Let us know what you find, please.
 

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NOPE, IT AIN"T, NEVER WILL BE ON AN ANALOG IGNITION SYSTEM. ONLY time the dial back is accurate is on an EFI setup where the EFI computer sets the timing curves, that is what dial back is designed to do, that is all it does, NOT ANALOG compatible...
Dave, I hate to disagree with you but that timing light pictured above came out long before EFI and computerized engine controls.
 

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OK, here we go, yet again, and it is way past old.

When we speak of a timing system that uses mechanical, and/or vacuum advance timing curves, that is an analog system, and when the timing is changed by those methods, the points, or reluctor and magnetic pickup make a spark, no lag, no computation time, it makes a spark then, right then, not a millisecond later, RIGHT THEN.

Now, comes along "dial-back". Why do we NEED a feature that recomputes a timing signal on a system that does not recompute it in the first place? WE DON'T.

What is "dial-back", anyway? Well, it is a program inside a timing light to recompute the spark AFTER a computer, such as EFI used inputs and computes a spark for an engine equipped with that computer. The "computation lag" creates an inaccurate timing signal to the ignition components from the time it takes to compute the degrees the system would make, and get that info to the module to make the spark. So, a computer timing system does alter real world timing to the point it is inaccurate as opposed to the direct fire no computation lag of the analog system.

Dial-back un-lags the computer computation lag time.

So, yes, dial-back is well worth it to get the timing right ONLY ON A COMPUTERIZED TIMING SYSTEM, but not even close to accurate on an analog system, THAT DOES NOT COMPUTER LAG COMPUTE TIMING.

Sorry to burst the bubble, but that is the way it has been all along, and misinformed by many since the invention of computerized timing curves, and over hype sales departments for dial-back timing light sales companies.

Dial-back is quite easy to fix on analog ignition systems, LEAVE THE DIAL-BACK AT THE ZERO NUMBER, DONE, FINISHED, WORKS CORRECTLY FOR ANALOG. Simple as that.
 

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Discussion Starter #54
Hi Dave,
I'm using a Pertronix II system in the distributor.... does that have any bearing on the dial back timing light? Or is it not relevant since it since uses the original vacuum advance system without any computer controlled ignition system?
 

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Discussion Starter #55
bumped initial timing up to 10deg @ 800 RPM and it’s steady. I’ll leave it here for now until I get a test drive.
 
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bumped initial timing up to 10deg @ 800 RPM and it’s steady. I’ll leave it here for now until I get a test drive.
I think you're really close to getting this resolved. I think ultimately you'll find that something in the neighborhood of 12* initial works great, then get your vacuum advance limited to about 10* total per Dave's instructions (with advance plugged in to full manifold vacuum) then use whatever bushing or whatnot is required to limit total mechanical advance to 36*-38*, and you're good to go.
 

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If the timing is computer controlled, there is no need for a vacuum advance, and with the COMPUTER CONTROLLED ignition timing, dial-back is accurate.

Dial-back IS NOT accurate on weights and vacuum advance distributors, because there is NO COMPUTER TIMING COMPUTATION LAG to compensate for.
 

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OK, here we go, yet again, and it is way past old.

When we speak of a timing system that uses mechanical, and/or vacuum advance timing curves, that is an analog system, and when the timing is changed by those methods, the points, or reluctor and magnetic pickup make a spark, no lag, no computation time, it makes a spark then, right then, not a millisecond later, RIGHT THEN.

Now, comes along "dial-back". Why do we NEED a feature that recomputes a timing signal on a system that does not recompute it in the first place? WE DON'T.

What is "dial-back", anyway? Well, it is a program inside a timing light to recompute the spark AFTER a computer, such as EFI used inputs and computes a spark for an engine equipped with that computer. The "computation lag" creates an inaccurate timing signal to the ignition components from the time it takes to compute the degrees the system would make, and get that info to the module to make the spark. So, a computer timing system does alter real world timing to the point it is inaccurate as opposed to the direct fire no computation lag of the analog system.

Dial-back un-lags the computer computation lag time.

So, yes, dial-back is well worth it to get the timing right ONLY ON A COMPUTERIZED TIMING SYSTEM, but not even close to accurate on an analog system, THAT DOES NOT COMPUTER LAG COMPUTE TIMING.

Sorry to burst the bubble, but that is the way it has been all along, and misinformed by many since the invention of computerized timing curves, and over hype sales departments for dial-back timing light sales companies.

Dial-back is quite easy to fix on analog ignition systems, LEAVE THE DIAL-BACK AT THE ZERO NUMBER, DONE, FINISHED, WORKS CORRECTLY FOR ANALOG. Simple as that.
Dave, I gotta disagree with you. Points setups and HEI units have lag in their systems, just like any other electrical/electronic system. Signals don't travel instantaneously, nor do voltage levels rise instantaneously. It's just simple laws of physics and limitations due to physics. Ya just have to design/build the system to compensate for those lag times, when possible.

Regarding the dial back timing light, I'm in agreement with OldCutlass. I personally don't use a dial back unit (all my toys have degreed balancers on them, so a simple light works just fine), but all timing lights use the plug wire current pulse as their timing signal. Unless you've got a special timing light that has an additional wire that plugs into the ECM, the timing light has no idea what's going on in the ECM, nor should it have to care. As long as the timing light can read the current pulses in the plug wire, it has the same RPM & 720* time information whether the ignition system is distributor controlled or computer controlled.

And with that measured time span between consecutive firings (720*), it's a simple task to make circuitry to delay the flash and convert the time delay of that flash into crankshaft degrees for display.

Now, the timing light being an electrical/electronic device, it will have lags in its circuitry, but a proper design will compensate for that in the flash delay timing/calculation circuit.

That's my experience and understanding of timing light operation. If I am missing a key item here, I welcome enlightenment or correction.
 

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So, "ZL", what else is new, you NEVER agree with me, because you have some sort of idiotic personal vendetta with me that only you cares about. And, you take it way too far with disagreeing with me on EVERYTHING, when you have been consistently wrong.

It doesn't matter the truth I write in these posts, you will never see the truth, only an opportunity to defame and flame me. That, you prove with every post done after one if mine, no matter the subject.

It ain't worth having a battle of wits with a completely unarmed person, so, I choose to not have one with you, being the person that doesn't get it.

OP, a PerTronix has nothing to do with computerized computation lag times, so, no heed to correct what isn't there, leave the dial-back off, please, sir.
 

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I sure hope you didn't check the timing with a timing light that has a "dial-back" feature on it that was set to read the EFI computer lag of the dial back, that is not accurate.
Hi Dave,


I've really learned a lot from your posts which I'm sure all of our Team Chevelle brothers appreciate.
My question is regarding the dial back feature on timing lights.


Have our Team Chevelle Brothers identified which dial back timing lights have the EFI delay
and which don't have it? I assume (and we all know what we say about that) the older vintage
lights probably didn't incorporate this feature because EFI was uncommon and the market for
them would have been minimal (not cost effective enough for the limited production)
while the modern timing lights do?


When my Chevelle is running again, I'll compare two of my old sears timing lights,
one without the dial back and one with the dial back. Then the following will tell me.


Verify the timing with the standard timing light-it reads 10* BTDC.
Using the dial back timing light set to 0 it should flash 10* BTDC.
Then dialing it back 10*, it should flash at 0*.

I don't think 0* BTDC is the correct designation, that's why I didn't use it.


Thoughts anyone?
 
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