[David Ray]

OK, everybody go put their "Whirling Dervish" costumes on. That'll help when everyone is spinning around in circles and gets nothing done.

There is a lot of good info in this topic, slogging, or, "whirling" through it will be a bit of a chore.

One thing NOT given is this, EVERY stock GM point type vacuum advance came from the factory with a degrees mark on the mounting plate of the vacuum advance that had the number of degrees added by that advance.....IF THE ADVANCE HAD THE FACTORY INSTALLED SHORT PIECE OF RUBBER STOP HOSE TO THE POINTS PLATE PULL PIN ON THE ADVANCE.

Lets take a look at this stop. Lets take an advance that shows "15" on the plate, and look at it with, and without the rubber stop bushing hose piece. With the hose bushing in place, the 15 degrees is correct, the advance will not deliver more degrees than that, period.

Now, lets let time, environment, weather take their toll, and have that rubber hose bushing rot off, fall off, or, have the same aftermarket vacuum advance installed, WITH NO RUBBER HOSE BUSHING IN PLACE. we now have 25 added degrees, and NOBODY knows why the same two advances have such different added degrees.

Adding the short section of rubber vacuum hose to the pull pin through its slot brings the advance back to having its 15, or whatever degrees the particular advance should deliver, right back to being good again. This section of regular rubber vacuum hose is roughly 1/2 inch long.

Then, the vacuum advance can be used once again, on full manifold vacuum, as it should have been in the first place.

Now, do you want to put a section of rubber hose on, to rot off again, or, do you want to go One Step Beyond? How about doing a steel plate that is adjustable, in two degree steps, that will never rot off, and never change unless YOU change it. It is a very low dollar plate, a hex head stainless screw and flat washer from the hardware store, a drilled and tapped hole, and done.

Full FREE instructions, with pictures, ask for them, works on both points and large HEI distributors, totally free, no ads, just fixing it right. And, if the advance dies later, this stuff goes right onto the next advance with the same simple single hole drilled and tapped that you do in YOUR garage..

Ask for them here: gmvacuumadvancemodifications@gmail.com

As far as adjustable vacuum advances go, the absolute best workable ones are the two Crane/FAST advances, they both work down to the lowest vacuum levels, and have the scroll stop plate inside the package with the kit, only need to drill, tap the mount plate, and the ultimate vacuum advance is ready to use. For large HEI distibutors, 99600-1, points distributors, 99601-1, stand alone scroll stop plate for use on stock GM and replacement advances, 99619-1.

And, last, but not least, as we see, there are a myriad of stock advances still available, with different vacuum and degrees parameters. ONE will work on YOUR application. Now, finding it might take a while. Consider that all those parameters can be a chore, and expensive. Consider as well, the Crane adjustable units, with the scroll stop plate re-positioned as in the instructions, gives you ALL those settings of those myriad stocker's, plus, EVERYTHING IN BETWEEN ALL THOSE SETTINGS. YOUR decision.

["QUICK-SILVER"]

Originally Posted by RocktimusPryme

https://www.napaonline.com/en/p/ECHVC1827 like this one, which is listed as starting at a low signal and only adding 5* at the distributor. 10-12 at the crank is likely where I want to be.

Double check those specs for the 1827.

First link shows 9° distributor with 9-11"hg.

Clay

[RocktimusPryme]

Yeah I meant 1703. I had initially put the 1827, then realized I misread it. I thought I had corrected the link.

https://www.napaonline.com/en/p/ECHVC1703.

I must have missed my copy and paste.

[HWYSTR455]

Basic rule of thumb is, when you switch to manifold vacuum from ported vacuum, you can't just dial the idle speed screw back. The best way to do it is limit the amount of vacuum, and give it more initial, as some were eluding to. 16-18 initial is a good area to start, with 8-10 degrees of vacuum, with your total mech advance limited to the target total of before you switched.

I usually base my initial on cranking speed. Use as much as you can with the starter/cranking CR without over-loading the starter.


.

[David Ray]

OG68, a simple question, just WHERE did you install the Crane scroll degree stop plate on the advance, where Crane said to do it on the rear mounting screw? Or, directly opposed to the pin???

There is a lot of good info regarding vacuum advances (or, what Ford called them, "Load Compensator", or, "Load-A-Matic"). It was mentioned that Ford had a vacuum advance in earlier distributors, such as the early flathead V8. These were the first L-A-M units, and not many people know how they actually worked. Conversely, if you see an early Mallory with a strange outcropping with a plate and hose nipple screwed to the side of that distributor, same operation.

If looked at, both those advances were virtually the same, they had the plate over a bored hole in the distributor body, and a piston, vacuum hose nipple, and spring. When vacuum was low, the piston ran into the body,, and high, pulled against the spring, to remove any drag tension against a ring of metal on the main shaft. this ring was a brake device to literally stop down a regular set of mechanical advance weights and springs.

When vacuum was high, piston was retracted from the ring, advance progressed to give degrees, and when vacuum was low, piston was allowed to drag against the ring, stopping down the mechanical advance retarding the timing.

Ford abandoned that in the late 1940's with the upright flathead V8, and all their inline 6's. so, when you see an early Mallory, pull that plate off, pull the spring and piston, and take a look inside one. amazing for th 1930's.

Now, anyone want to tell me just why a stock vacuum advance that should only give 15 crankshaft degrees gives close to 25 degrees when put into place and service? It is marked right there on the vac adv mounting plate, "15".

Well, it really isn't a secret. the factory points c=vacuum advance did only give the degrees shown, but, it did so with a small length of regular rubber vacuum hose fixed over the pull pin on the advance, to stop the pin travel in its slot. Most of us have never seen that rubber bushing, it was either rotted and fell away long before we first saw the distributor, or, a new replacement vac adv was fitted, that never had the hose bushing in place, ever, and nobody else knew about it, either.

Without that simple half inch of rubber hose on th pin, the advance delivered way too many degrees of timing. so, what to do? we don't want to repeat history, with a bushing that will rot off. EASY FIX.

How about a steel stop, either home made for a set degrees stop, or, with one sple drilled and tapped hole, a stand alone Crane stop plate, and a hardware store hex head machine screw and flat washer, mount a plate that will not rot away, and give you 2 degrees per serration degrees adjustment, that can be done to any stock or adjustable GM style vacuum advance, points or HEI.?????

Yes, this IS the scroll plate that comes with any and all Crane adjustable vacuum advances, and is available stand alone. the Crane p/n for the stand alone plate is 99619-1, and any speed shop, and online have them. As said, they also come inside the Crane/FAST full adjustable vacuum advance kits as well.

Those Crane plates just need to be mounted correctly to the advances, NOT the way Crane/FAST outlines. The Crane method loads the spring in the diaphragm harder as the degrees are reduced, to the point they cannot be reduced after a certain point, so no matter what is done, the vacuum level is too high to allow the advance to work. Or, the way outlined in the package, separating both vacuum, and degrees adjustments, so each is totally not interfering with the other???

The Crane plates will fit stock GM vacuum advances as well, so, when you find one with the correct vacuum to match the cam, if the amount of degrees is too much, stopping the degrees down is simple, easy, fast, DONE.

If anyone wants a complete info package on just how to do the plate install CORRECTLY, those instructions, complete with pictures are totally FREE, NO ADS, NO frills, just how to do it right, ask for them, they work on both points and large HEI. ONCE AGAIN, THEY ARE ABSOLUTELY FREE, NO CHARGE.

gmvacuumadvancemodifications@gmail.com

When this is done, most carbs that are idling with too high an idle setting, will be able to close the throttle plates down to the point the idle transfer slots are in the correct relation to the closed throttle, so they work right.

[Kenth]

Dave, you wrote this in "the other topic", can you give an example of a vehicle using venturi vacuum for the vacuum advance (load compensator)?
I´m trying to understand what you mean by "second acceleration advance curve".

Me:
"Please explain how a vacuum operated load compensator would ADD timing at acceleration? "

Dave:
"Welllllll, as we all know, full manifold vacuum REDUCES upon engine acceleration, because engine vacuum reduces as throttle position is increased, during engine acceleration. So, there would be no additional timing, no second acceleration curve as this occurs.

PORTED vacuum is moot at low to no load, and high engine vacuum levels, such as no to light load cruise, and when the engine is accelerated, vacuum is created at the ported port, bringing into operation, the 'load compensator', forcing it to work completely opposite of how it should, adding vacuum advance degrees upon engine acceleration, CREATING A SECOND ACCELERATION ADVANCE CURVE ADDED TO THE MECHANICAL CURVE, MAKING TWO DISTINCT ACCELERATION CURVES."

[Formulajones]

Originally Posted by dataway

Kind of makes you wish someone produced a servo control VA ... vacuum sensor to a small microprocessor .. to distributor mounted servo. Dial in your start, climb rate and max. I found you can map a particular can pretty easy with a hand vacuum pump ... at least fairly easy to find start vacuum and when it's maxed out.

They do, the MSD digital E-curve distributor allows you to set the mechanical curve electronically as well as the vacuum curve electronically for extremely precise adjustments.

And yes I bench test the vacuum advance units here to find the points where they begin and end with vacuum applied so I can dial in what I want. I simply find that limiting the travel like I pictured previously by welding the slot is just as easy for me as drilling and tapping in front of the rod and installing a key like mentioned above. Both accomplish the same thing, I just prefer the permanent method because once I have it set and working there is no need to go back and revisit it.

If you're on the cheap, and you can't weld, yet you want that limiting key, you don't even need to buy those keys. I use a penny, file my slots in it, drill a hole and screw it down in FRONT of the rod pin. It only costs a penny.

And as mentioned it's important to limit the travel from the FRONT, in the direction the pin moves. Not from behind the pin as so many instructions illustrate.

[RocktimusPryme]

On the electronic limit part, other than expensive CD boxes there was this guy http://forums.maxperformanceinc.com/...d.php?t=832333

I think it’s super interesting, but there aren’t enough buys or reviews for me to want to jump on it. I’ll be the guinea pig for a $25 vacuum can but not that. I would like to see a forum member use one and report.

[David Ray]

Yes, I fully outline in the vacuum advance stop package, with install instructions and pictures that I have offered for the last 20 years for absolutely FREE for the asking.

I have outlined well past how to do it for decades on boards all over the place, and quite a few have actually benefitted from the info, most just sit back and listen to other info that doesn't work.

It costs NOTHING except a bit of time to look at what is offered to actually fix the issues regarding vacuum advance.

And, yes, some adjustable vacuum advance people do not outline how to stop down degrees of tming without changing the vacuum pull rate of the advance, MY INSTRUCTIONS SEPARATE THE DEGREES ADJUSTMENT FROM THE VACUUM ADJUSTMENT COMPLETELY, and it is so simple, ONE drilled and tapped 8/32 hole, done, adjustable.

The stop is a speed shop item, not expensive, the hex hear stainless machine screw and flat washer, directly from YOUR local hardware store, done, simple. and, can be used on adjustable advances, AND stock ones, because if you find the right vacuum rated stocker, there is no guarantee that stocker will have the right amount of degrees to work.

There is even a video circulating to "adjust the degrees" on an adjustable vacuum advance by turning the vacuum screw to get the correct amount of degrees, and that is DEAD WRONG. turning the vacuum adjustment screw to restrict the amount of degrees ends up stopping the vacuum screw down do tight, the advance does not function, in about two or so full turns of the screw.

The only way to do it is to separate the vacuum adjustment and the degrees stop adjustment. My instructions do exactly that.

Please do not go to war with me over this, I wrote the book on how to fix it correctly, and even if you don't care to do it, others will, with the same result, it fixes the problems. Simple as that.

In the last 5 minutes, I have sent 3 sets out to persons reading these topics about properly setting up vacuum advance that came to it from this board and topics. I prompt those, and amyone else to post before, and after results frm them, if they so desire to do so. They will be their own judges as to whether I am the moron some have made me out to be, or, the person that helped them FINALLY get it right.

Kenth, PLEASE, you do not have it right, and I am just out of patience to go over and over, and..over it , yet again, and again, and again with only you. We have been over this some years ago, when you kept insisting the wrong way was the right one, and you did what you want to do now, do any and everything to pick my info apart, and your efforts will still not work. And, I never had to prove it, those that did what was in the instructions did it for me, by doing those instructions and procedures for themselves..

[OG68]

Dave, I installed it following your guidelines.

[Kenth]

"Quote:
Originally Posted by David Ray
WRONG.

Since ported vacuum is taken further up the throttle bore, well within the smallest diameter of the venturi, vacuum is created there, to pull a vacuum advance diaphragm into adding timing during acceleration, or, make a second acceleration timing curve..

The vacuum signal at the base of the carb at WOT is extremely low, to completely NIL, so, no vacuum pull, no vacuum advance timing on full manifold vacuum sourcing at full throttle, NO secondary acceleration timing curve..

VAST difference with vacuum levels between full manifold and WOT ported sourcing.

Try driving around with TWO vacuum gauges connected, one to each type port, as I have, many, many times."

Dave, i can assure you i know the difference between the ported or the full manifold source for the ignition vacuum advance, and why either is used.

And, wouldn´t it be easier for you to just give an example on any carb or engine that uses a ported source to add a "second advance curve" from the ignition vacuum advance, instead of twisting and turning my words against me and make up fantasy statements?

Thanks.