Timing - BTC, ATC and carb

[440Magnum]

Originally Posted By: SteveSRT8
OMG, I can't believe the advice here!

It's not a vacuum advance it's actually a vacuum RETARD! It pulls timing under throttle.

The weights/springs setup inside the dist advances timing based on rpm.

Pulllleeeeaaaze!

At least Skygod got it right.


You're the only person I've ever heard call it "vacuum retard." Its normally called "advance" because the de-facto advance setting is determined with it DISCONNECTED, and it applies additional advance when the engine can generate enough ported vacuum to overcome the spring pressure in the can and cause it to advance even further. A single-port vacuum advance NEVER retards to less than what the mechanical base timing mechanism dictates.

Back in the early days of 1970s smog motors, there were dual-port systems that would both advance AND retard based on the relative vacuum on either side of the diaphragm, controlled through a rats nest of hoses and valves that acted according to ambient temprature, throttle position, etc.

 

[SteveSRT8]

The reason I called it "retard" is because in operation that's exactly what it does. Vacuum pulls it up tight (advanced fully) and then as you give the car throttle it retards the timing.

Gosh, you must have had a lean burn Chrysler.

 

[OVERKILL]

Originally Posted By: SteveSRT8
The reason I called it "retard" is because in operation that's exactly what it does. Vacuum pulls it up tight (advanced fully) and then as you give the car throttle it retards the timing.

Gosh, you must have had a lean burn Chrysler.


Depends on whether it is ported or regular vacuum Steve.

Ported vacuum increases with airflow through the carb, so it increases timing with throttle.

 

[440Magnum]

Originally Posted By: SteveSRT8
The reason I called it "retard" is because in operation that's exactly what it does. Vacuum pulls it up tight (advanced fully) and then as you give the car throttle it retards the timing.


Wellll... no!

Remember, its controlled by PORTED vacuum, which is tapped ABOVE the throttle plates, but near the plate edge so that the plate position still affects the velocity past the poort. There is only vacuum available to the vacuum advance mechanism when there is high air velocity past that port in the carb- not the same as manifold vacuum. At idle... zero vacuum advance. At part throttle cruising on the highway- full vacuum advance. Coasting down a long hill throttle closed- zero vacuum advance. Climbing a hill- reduced vacuum advance, but not zero. WOT- zero vacuum advance.

Originally Posted By: SteveSRT8
Gosh, you must have had a lean burn Chrysler.


Thankfully, no! But Dad owned a couple. They used a mechanical vacuum modulator vary a potentiometer input to the PCM. Franken-timing.

 

[SteveSRT8]

You and I are saying the same thing. OK you win.

Note: under heavy load it PULLS timing! That is all. Low revs, open throttle, you get retarded!

 

[sasilverbullet]

I think I found my problem. I'll be able to confirm it later tonight when I put the new distributor in WITH points!

See the area I have circled in red? Where the points come VERY close to the vacuum advance arm? And notice how the points "rotate" on the screw that's at the other end? Well the Pertronix Ignitor II I had installed pivots on the screw near the red circle. Two things happen wrong - 1. there isn't the required clearance for the Ignitor to magnetic sensor, and 2. It prevents the vacuum actuator from returning to it's original position - hence the excessive pinging. [censored], what a waste of money! I have a call into Pertronix and they're trying to figure out what the fix is.

[img:left]http://www.thelincolnforum.net/phpbb3/download/file.php?id=12228&mode=view[/img]

 

[sasilverbullet]

Confirmed - the car runs fine, no pinging, with a stock coil and points.

So here's my problem with the Ignitor II...see the plastic feeler gauge? It's the .30 gauge they give you in the box. So with
the proper clearance, see how (circled in red) the screw hole is not accessible unless I do some major modifications to the
Ignitor II unit. As you can see from the pic I've already ground the Ignitor II some to get better clearance.

Here's a close-up of the problem with the Pertronix Ignitor II -

I've already been on the phone with Pertronix, they're willing to swap my unit out for a new one, but will not give me a
refund because of the way they sell their product. I can then get back with my original flea-bay seller to see if he'll give
me a refund on the "new" unit they sent me. Crud.

So what to do? I've already spent $160 on the Ignitor and $45 on a MTD coil - for what?

Any ideas folks?

 

[440Magnum]

Pertronix is a nice idea, but I've never been all that excited about sticking the electronics inside the distributor. Are you sure you've got the right Pertronix module for the particular distributor you have?

You can talk to your E-bay seller and try for money back. If that doesn't work then if I were you, I'd take a deep breath and look at possible ways to modify things to get it to work, now that you have a different working distributor to use while you fiddle with this. Some more grinding on the pertronix mount, or removing the advance plate from the distributor and drilling/tapping a new screw location might do the trick.

 

[sasilverbullet]

Originally Posted By: 440Magnum
...some more grinding on the pertronix mount, or removing the advance plate from the distributor and drilling/tapping a new screw location might do the trick.


hmmmm, that just might be doable! Thanks for the suggestion...

I definitely want to put the Pertronix and MTD coil back on - with points, even though it's all running fine, it just doesn't seem as "peppy" as it did with the Pertronix and MTD coil.