66 327 Vacuum Advance Issue

[William B.]

Gentlemen,

I purchased a 66 327 300 hp that had a pertronix ignition kit installed. While doing some tune-up checks, I discovered a small bearing, the size of a BB, inserted into the vaccuum advance rubber hose where it connects to the vaccuum pot. It completely blocked the vaccuum from the carb. Is this normal for a car with a pertronix ignition installed? Is someone messing around? I don't know enough about an electronic ignition to know if this is normal. The car seemed to run normal. Don't want to remove the BB if it is required for this type of iginition. Please educate me.

Thanks

Ken

[Duke W.]

Re: 66 327 Vaccuum Advance Issure

This issue has been discussed in great detail in just the past couple of days. Take a look at recent threads on engine performance, idle, distributors, and you might even consider spending a few minutes looking for relevent threads in the archives.

Whether or not you have points or an electronic switch has absolutely no bearing on what makes for a proper spark advance map.

Duke

[Gene M.]

Re: 66 327 Vaccuum Advance Issure

The vacuum advance should be operate even with the Pertronix.

[William B.]

Re: 66 327 Vaccuum Advance Issure

Thanks all. I understand the process of timing a normal points auto. I was worderning about the BB size blockage with the electronic ignition. There was where I needed your experience. Thanks again.

Ken

[Stuart F.]

Re: 66 327 Vaccuum Advance Issure

I have the Pertronix II kit in my 63 L-76. I also use a B-28 VAC with full time manifold vacuum. I've had this setup for at least 10 years. The only change I made was upgrading from a basic Pertronix unit to the II version which only required re-wiring for a full time 12 volt input instead of using the ballast resistor. Why anyone would plug the vacuum line is beyond my comprehension. Does anyone have an answer?

Stu Fox

[Russ S.]

Re: 66 327 Vaccuum Advance Issure

I am no expert here but I am of the understanding that if the distributor has been set up for mechanical advance (different weights and or springs) then you don't need the vacuum advance, This could explain why the bb is in the hose.

The vacuum advance should be operate even with the Pertronix.

[Rich G.]

Re: 66 327 Vaccuum Advance Issure

As Duke said, take the bb out, get the correct can based on his two inch rule. I have a 66 350 horse with the pertronix kit and before I saw the light I found it ran better at cruising speeds with the advance line plugged. It would surge while trying to hold a constant rpm on the road with the vac hooked up. Of course in this configuration there is more heat generated at idle. Once I got the correct can things work correctly.

Rich

[Joe R.]

Re: 66 327 Vaccuum Advance Issure

Russ,

The engine requires proper timing under all combinations of vacuum and RPM. The vacuum advance takes care of the vacuum side. The distributor weights handle the engine speed side. The only time the vacuum advance hose should be plugged is while setting idle timing. I believe John Hinckley wrote an excellent article on this very subject. Look on Barry and Linda's Vette tech page.

Joe

Edit - the article is here:

http://lbfun.com/Corvette/Tech/vettetech.html

Click on "Timing and Vacuum Advance"

Select "Timing 101"

[Duke W.]

Re: 66 327 Vaccuum Advance Issure

I am no expert here but I am of the understanding that if the distributor has been set up for mechanical advance (different weights and or springs) then you don't need the vacuum advance, This could explain why the bb is in the hose.

I am an expert at setting up spark advance maps and your "understanding" is dead wrong for any reasonably configured road engine that didn't have to meet emission standards.

The only guys who disable the vacuum advance are named Bubba.

Duke

[Stuart F.]

Re: 66 327 Vaccuum Advance Issure

Bubba here;

On my very first Chevy V8, a 55 back in 1956, I had a tipping advance plate problem. Upon acceleration, the vacuum advance would cause the plate to tip throwing the dwell way off and limiting the rpm's big time. When I disconnected the VAC, and advanced the initial timing, it ran like a scared rabbit (this was a base 162 hp V8 w/old style distributor).

Since that bad experience I have been paranoid about the same thing happening to my large cap distributors. Therefore, I have been using Dyna Flyte ball bearing plates (no longer available) starting with my tri 5 Chevy's until today in my 63 L-76 Vette.

Stu Fox

[William C.]

Re: 66 327 Vaccuum Advance Issure

the plate retaining clip had to be missing for what you have described to occur. A good lesson on check for the cause of a problem before talking to "Bubba" about a fix...

[Duke W.]

Re: 66 327 Vacuum Advance Issue

I had all kinds of problems with premature ignition breakup on my 340 HP '63. After talking to "experts" I now know that those guys were clueless.

I finally gave up on the single point and bought/installed the TI from my college classmate who was taking apart the 12-mile L-88 in 1968.

In the mid-seventies I took apart the single point and found that the breaker plate "wobbled", but it was properly retained with the wavy C-clip. After overhauling/blueprinting it (new breaker plate, shimmed up end play, 32 oz. points) it ran to 7000 without a hitch on the Sun distributor machine in the Air Force Auto Hobby shop.

The new breaker plate fit snug and didn't wobble, so I guess the original was somehow defective from day one.

After the TI went TU for the second time I pulled it out, repaired it and reinstalled the single point, which worked flawlessly and didn't have a sudden habit of quitting with no warning.

Those old Delco distributors were indifferently assembled and worked okay on the grocery getters, but needed a little TLC on a high revving applications. Plugging the vacuum advance was on the the "fixes" that shade-tree mechanics did at the time, but like Clup said, it's better to ascertain and correct the underlying problem rather than resorting to a bubba fix, but I'm sure we all did a few of those back in the day, and a lot of guys are still doing them, today.

Checking for a snug, wobble-free breaker plate is standard procedure now, but unfortunately I know of no service replacements for the ...047 breaker plate that was used on millions of single point distributors. The last distributor I overhauled - a L-79 a year ago with about 80K miles - had what appeared to be the original breaker plate, and it fit nice and snug with no wobble.

I ran across a guyw with a NOS Niehoff ball bearing breaker plate a few years ago, and I had never heard of such an animal. We tried to install it in the distributor, but some modification to the distributor was required, so we decided not to.

Duke

[Domenic T.]

Re: 66 327 Vacuum Advance Issue

I have a few aftermarket distributors that have no provisions for vacuum advance. Don't ever remember using them or if they were for race only application. They are mechanical advance Mallory. Can some one refresh my memory as it seems that the knowledge is on this thread.

DOM

[William C.]

Re: 66 327 Vacuum Advance Issue

Race only, and even then you need to know what the characteristics of the actual advance curve are...

[Stuart F.]

Re: 66 327 Vacuum Advance Issue

How about the old W&H Dual coil? I had one of those animals for awhile. My most vivid memories of it was that it had a maroon cap, aluminum housing, and I needed a 4 cylinder sending unit for my Sun tach. That distributor too was without a VAC.

With my Dyna Flyte plates, they worked fine with just one set of points, but when I went to electronic ignition (including my current Pertronix II), there is a nub on the plate surface that is there to locate the points. I have had to grind them off with my Dremel tool (very carefully so as to keep the metal dust out of the ball bearing rings). The one I have on the shelf is kept oiled and wrapped in oil paper. You should see how sweet these run on a Sun distributor machine. I set up the distributor from my 63 many many years ago on a Sun machine. Other than changing the VAC, following Duke's 2 inch rule, and an occasional cleaning and inspection, it has performed flawlessly ever since.

Stu Fox