vacuum advance with electronic ignition

O

operaroverman

Member
Good evening all,

I have a petronix ignitor system replacing the points in the distributor in my 1974 3500 auto. The chap who fitted it declared the vacuum advance redundant and wound the adjuster drew shut on the dizzy. This was nearly a year ago, and the car has run OK but not as well as I hoped. Could someone please tell me if this was the right thing to do or not? I have now been told that the vacuum advance is still necessary, and have discovered that the membrane was punctured by the adjuster screw so I have an air leak!

Many thanks,

John
 
The vacuum advance is an economy device. Do you want better economy? Or will you accept that the air leak in the vac unit diaphragm will give slightly better economy at the expense of performance due to the weak mixture.

"Chap" is probably the best description of the competence of the bloke who fitted it I'd say.
 
The chap is talking through his hat.

That type of ignition only replaces mechanical switching with electonics. I'm not sure why that would render any device that alters timing redundant.
 
Thanks chaps!

I will buy a new vacuum unit, have it fitted, and have the timing set up accordingly. Hopefully everything will then be well!

John
 
Hi John, the chap who fitted it was me.
You seem to have vacuum advance and dwell confused.
The dwell adjuster was wound in as part of your installation as dwell is set electronically by the ignitor module. This is standard Pertronix procedure.
Vac advance was not touched to my memory and I can't see how it could have been damaged from the conversion.
Jim
 
As Jim says, with the Pertronix set up, the dwell adjustment is wound right in, the vacuum advance is still in operation.
 
Sorry not to reply for so long on this thread!

First, Harvey, an unintentional slight to you over use of the term "chap'! Thank you for your advice.

Second, Jim, I have PM'd you. Thanks for posting.

I guess I have confused vacuum advance with dwell. I assumed that winding the adjuster shut rendered the vacuum advance inoperative...
 
I hope everyone is enjoying the hottest day of the decade!

My V8 is now running very sweetly indeed! Thank you Jim for setting me straight on the difference between vacuum advance and dwell. I now understand why you wound in the dwell adjuster when you fitted the petronix ignition system. With the points gone, there is no longer any adjustment to be made! Everything was set up as it should be. My problem was a perforated vacuum-advance diaphragm. A new unit from Wadhams has been fitted to the dizzy and all is well. Mine is a low-comp engine and I have had the timing set to 4 degrees before TDC to eliminate almost all pinking, but give myself good performance. My carbs were rebuilt and balanced by Pete Palmer in Godalming over a year ago, and everything there is obviously still in excellent shape! The car is now running, idling and driving extremely well.

I entrusted this job to Orchard View Classics in Yalding near Maidstone, and I would recommend their services. See my other post to discover how they seem to have cunningly eliminated my fuel-vapourising issues!

John
 
operaroverman said:
Thank you Jim for setting me straight on the difference between vacuum advance and dwell. I now understand why you wound in the dwell adjuster when you fitted the petronix ignition system. With the points gone, there is no longer any adjustment to be made! Everything was set up as it should be.
Click to expand...

I'm glad we got that little misunderstanding cleared up, because Jim is an exceedingly fine chap, and I mean that in the nicest possible way....
 
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