Vacuum advance/retard help...

P

PhilipTheBavarian

New Member
Messages
5
Reaction score
1
I have a 72 e3 with the duel weber 32/36 conversion and no emissions. My question is concerning the vacuum advance and retard lines from the distributor. Do I need the vacuum retard line?

Thanks, Philip
 
Leave the retard side of the vacuum advance open. Otherwise the advance side has to pull against a sealed chamber....
DaveG
 
DaveG said:
Leave the retard side of the vacuum advance open. Otherwise the advance side has to pull against a sealed chamber....
DaveG
Click to expand...

Ah, an interesting point. My coupe has had a plug on the retard side of the chamber mounted on the distributor since I bought it in 1989. It had Zeniths on it at that point, though I have since converted to Weber 32/36's. It has always seemed to run OK, and the multiple professional mechanics who have worked on it over those 23 years have never commented on the plug. Still, I see DaveG's point. I'll try removing the plug and see what happens.

My guess is that most of the advance curve is determined mechanically (i.e., by the weights & centrifugal force), and the vacuum stuff doesn't do much either way.
 
Last edited:
On a related note... With the Weber 32/36s, is it recommended to run the advance off of a teed connection from both carbs?
 
manifold vacuum

shouldn't be used for the distributer advance. You want a ported source which is above the butterflies. Otherwise, you're timing is way advanced too early which can lead to things best left unsaid.
 
I run the advance for my Zeniths off a teed ported vacuum. Not sure if it matters, but makes me feel good that I am getting strong vacuum there.

sreams said:
On a related note... With the Weber 32/36s, is it recommended to run the advance off of a teed connection from both carbs?
Click to expand...
 
Clarification?

61porsche said:
shouldn't be used for the distributer advance. You want a ported source which is above the butterflies. Otherwise, you're timing is way advanced too early which can lead to things best left unsaid.
Click to expand...

Should the vacuum source for the advance be above, or below the butterflies? This digram seems to depict below?

http://i25.tinypic.com/s1mhys.jpg
 
That diagram

is for an EGR equiped coupe and should be in a museum of failed emission attempts with all the heads that BMW replaced in the class action of let's not do that anymore engineering.

Your carbs should each have a port. It's located on the head side of the carb.Use that for your advance on the distributer.

Not anything from the manifold to the distributer.(unported)

Now if you live somewhere cold and your air cleaner / heater flap is working then that's something to discuss. Check yours. I long ago blocked mine open on the factory air cleaner.

Tip- using hose or piping create a vacuum balance tube between the manifolds without any T. It does exactly what it says- smooths out the vacuum pulses/ firing which smooths out the carb signals which smooths out your idle/ running.
 
FYI
The main reason to use ported vacuum for the vacuum advance is to allow a little smoother idle.
As the throttle cracks open the difference between the manifold and the vacuum port disappears.
Vacuum advance is really used to improve part throttle driveability and help the gas mileage a bit. At full throttle, the vacuum advance is inactive, as there is very little difference between the manifold and the ambient pressure at full throttle.
DaveG
 
Source

I only have two sources in the current setup: each of the Weber 32/36's have a single vacuum post at the base of the carb(s) just above the base. The other port, and cuurently plumbed source, is in the aft intake manifold itself. The solenoids(?) on the firewall have been bypassed.

There is no vacuum source port on the forward intake manifold.

Where physically should i pull the distributor advance vacuum ?
 
Base

of the carb. The way you can tell is that at idle there would be no vacuum. As the carb gradually opens that's when vacuum appears and advances the distributer.
 
I run my vacuum advance on full manifold vacuum to keep the engine running cooler and more efficiently at idle. I use a tee connected between the manifolds, and have a vacuum gauge on my dash.
Ported vacuum was an early smog band-aid. Here's an interesting treatise on timing and vacuum advance by an old GM engineer:

http://www.corvette-restoration.com/resources/technical_papers/Timing101.pdf
 
Distributor cleaned / coil checked

I removed the distributor (set the silver ball to OT and rotor pointing to the static alignment mark on the distrb case, prior to pulling. The vacuum regulator is both leaking from the bellows and armature stuck/v difficut to move.

Removed the articulating plate were the Pertronix is now installed, cleaned/lightly greased the top and bottom plates. The mechanical advance looked and functioned correctly. Springs intact, and good movement.

While waiting for the new vac adv/retard, checked the coil (clearly an after market Autozone cheapie, wrapped w a piece of cardboard, no joke, to give it more girth to fit the stock mount bracket). Brand "Diamond LB-89 12v Japan 12305". Removed from the car, it statically is 3.1 ohms. It was / is curently wired in the car in series with the ballast resistor. I think this is not right? Can i ask for a confirmation that the 3.1ohm coil should (or should not) be wired directly to 13.4v?
 
You must log in or register to reply here.
Back
Top