Finally got the damned screws out of the distributor to swap the vac adv to a shiney new one....I expected a timing change with the hose connected...still nothing
I have the hose on manifold vacuum, front carb, Edelbrock 1405, as facing front of carb, right port....even checked the Edelbrock website to make sure I was right...with finger over hose, I have vacuum at idle, and hooked the new canister up before install and the lever pulled all the way back when applying vacuum...when I had the old one out, the adv (in dist) lever is working smoothly, and appears to be causing the timing to advance if I move it back and forth....
How much advance should I expect from the vac adv and any reason why it isn't advancing??

 

what is the vacuum level of your motor at idle. put a vacuum gauage on the line and measure it.

What are the specs of the new vacuum can you just installed?

vacuum is measured in INCHES HG.
If for example your motor is only producing 12-13 in/HG but the vacuum can specs require 18 in/HG to max out than the vacuun can would not be the correct choice of can.

Since you are using a full manifold vacuum source, you need a can that will pull in full vacuum advance 2" below the manifold vacuum at idle.
So, if for example you get a vacuum reading of 14 in HG when you hook a vacuum gauage up to your vacuum port, you would than need a vacuum can that pulls all in at only 12 in HG.

Best bet would be to read Lars paper called detailing about vacuum advance and also lists all the specs of various models of different vacuum cans so you can select the proper one for your motor.
I have his tech paper on my website tech articles page here:
http://69.253.166.197/page1/page65/page65.html
The article you want is called "Vac Adv Specs.pdf"

 

Yeah, I attempted to read Lars paper on the advances and well, my eyes started to blur and, well, I jumped to the bottom where the specs are...
I bought a standard vc1838 that Lars suggested to me...BUT...these are not stock carbs, so I guess it all depends on the "actual" vacuum reading as to what I should be using in there....how much do these vacuum gauges go for??
$$$$$$$
And additionally, is there a way to make what I bought work?

 

yeah, it takes a while sometimes to understand this stuff and have it sit well in your head so that it makes sense but it's not really TOO bad if you take your time and read it carefully and think about the system and how it works. It took me a while before I felt I had even the most basic concept of it.

Vacuum gauges are expensive. you should be able to get one at your local auto parts stores such as a NAPA, Auto Zone, or whereever. I think I got mine at my local NAPA for around $20 or so.

Mine only came with a single rubber hose to plug into a vacuum port so I also picked up an extra length of rubber hose and a "T" fitting so if I need I can "T" into an existing vacuum line to check levels.
all you need to do it plug the gauge up to your vacuum port and read the level it givies you at idle since it's at idle that you are concerned about having the vacuum can give you full vacuum advance.

looking at the specs of the VC 1838 can that Lars recommended it should work fine I'd imagine (not that Lars would be wrong very often! )
According to the specs it starts to pull in the advance at only 7-9 in HG and pulls the advance in fully by 12 in HG. It supplies 7* of distributor advance which is the same as 14* engine advance (distributor advance is one half of engine advance).
If your distributor is set for 36* total timing the vac. can will supply another 14* to give you 50* total w/ vac advance so it should be fine.

As long as your motor is suppling around 9-11 in HG it should be fine if i'm not mistaken.

BTW, let me just confirm. You got no timing change with the new can connected as opposed to the old can connected?
Are you getting a change with the new can connected than with the new can disconnected? In fact, you should be able to quickly check the function of the new can by simple disconnecting the vacuum line from it - when you pull the vacuum hose off the can are you seeing a decrease in your idle speed?

 

I'm sorry...here's the story....after setting the timing the Lars way, I noticed that I had no change of timing with the hose on the vac adv or with it plugged, so naturally...must be a bad can
Then, I couldn't get the screws out and after all different ways to turn them, I managed to loosen them, went and got a new can and installed, first testing the new can by attaching vacuum to it and it pulled back just fine, so in it went...then started the engine and no change from the new can....
So here I am...asking questions...I was wondering, if I elongaded the holes on the new vac adv, so as to pull it outward more, might that work? That way, the rod would pull back farther inducing more advance..a little at a time until I get what I need???
I know, I know...grasping at straws, right?

 

20-30 bucks it what i payed max

 

ok. you have tested the vacuum port with your finger over the hose and confimed you ARE getting vacuum at idle so you are on a full manifold vacuum source there. Fine.

You tested the new can and it pulls back when hooked to the vacuum hose so the new can is working. fine.

you just aren't getting any additional advance on the timing with the can installed on the distributor and hooked up. Right?

Just making sure I'm understanding everything correctly so far........

What I would do it is this:

1. get the vacuum gauge and measure what level of vacuum you have at idle off that vacuum port.

once we know that we can compare it to the specs on the vacuum can and make sure you have the proper can.

2. you say you set up your timing as per Lars paper. WHAT is your timing giving you now.
what is your initial timing? what is your total timing and at what rpm is your total timing all in?

BTW, it could also be a good idea that when you get your vacuum gauge and get an extra length of hose and a "T" fitting, pick up yet another long length of vacuum hose. You can use this long one to hook up the vacuum gauge and run it to the cockpit of the car. This would allow you to hook up the vacuum gauge and be able to check and monitir the vacuum level you get while actually driving on a test drive so you can check your vacuum level while driving with the motor at easy cruise speed. This means not accelerating or at WOT, but just easily cruising down the road. Having this vacuum level measurement is handly also besides your vacuum level at just idle.
At idle you may have lets say 14 in HG of vacuum but at easy cruising speeds if your vacuum level is only 8 in HG and the vacuum can rewuired 12 in HG (which the VC 1838 does) than you won't get any vacuum advance.

Get the vacuum gauge and measure the levels so we can check things so far and than we can try to determine where you stand and attempt to get you working correctly.

 

You mentioned in your post about a front carb, is this a dual quad setup with Carter AFB`s?

 

Fascinating thread. I have been following this for some time now and it gets more interesting as it goes along.

 

OK..lemme answer Ironcross first...yes, dual quads...Edelbrock 1405's..
Now...assuming I dump MORE money into her, and get the vac gauge...then we would know...but assuming this is the correct can for a stock 350, and assuming the old can "was" bad and didn't work for , say 50,000 long miles and years...the new can should work...could I possible have a problem with a rusty advance lever "in" the dist? I mean, I doubt that can has a "lot" of pull if the mechanism is even slightly frozen...ya know? It just seems to me things shouldn't change so much that I would need a different can then stock...it should have worked and advanced timing stock in 1976, why isn't it working now...you know? I just am trying to avoid complicating something simple if at all possible...your thoughts...I think testing the old can would be necessary..I haven't done that yet..that may give us some answers...

 

If you have AutoZone where you live they have a tool loaner program
Ask them for the Vacuum pump.. It is a pump which is great for testing for vacuum leaks and it also has the gauge which you need.
It's $50 to rent and when you bring it back you get your entire $50 back
So........ It wont cost you a dime.... Period

 

Dual quads or not, Vette or something else, pictures are sometimes worth a thousand words and therefore no need for a pissing contest. {1st amendment free speech discriptive word} Observe the picture links below. Both engines can and are street driven delivering a bunch of HP and basically observe that you can run without the can hooked up, contrary to the experts

 

Wally
no one is saying that motors CAN'T be run without a vacuum advance system in place.

Everything I ever read or learned though from people such as JohnZ and Lars is that on a street driven car having the vacuum system is preferable to help the motor run more smoothly, inprove idle characteristics, improve throttle response, keep engine temps down, and a host of other reasons.
I myself never suggested, not read any posts that claimed that without the vacuum system the motor wouldn't run or it can't be street driven - only that there are benefits to having the vacuum system in place on a street driven car.

 

I have a mallory tach drive distributor and it doesn't even have the vacuum advance or a hole to install one. I wish it did just so the car would idle better. Its a nice distributor but I will eventually pull it and put something with vac advance in its place. Also I dont believe boat engines use vacuum advance either. The 350 in my boat doesn't. Others I have seen dont either.

 

Hi Barry, figured that would get someones attention. that a pure stock low HP street piece should and will be better off with with the vacuum. However most of the questions are with and about some sort of aftermarket performance stuff attached to a stock style engine and as a result come up with all kinds of related problems and most of the time go in the wrong direction to try a fix. Timing is critical and many dont have a clue. So, just make it all in at 3000 and a total 36+-. They do not overheat, idle is good, and so is the gas milage unless the combination is all screwed up from the beginning.

PS, as a stock engine example, my 62 FI piece runs from it`s idle of 800 RPM`s to whatever, a 170-180 temperature, and gets 16-18 MPG with a 4.56 gear and there isn`t even any provision for a vacuum advance from the factory. And that sucker is a real joy to drive. It don`t skip a beat

 

Wally
how in the h*ll do you get 16-18mpg on your '62 with a 4.56 rear end?

my '65 327/365 L76 (all stock including the 30-30 cam) doesn't get that good of a mileage and my rear gears are *only" 4.11's.

 

Biggest reason Barry is that you dont have a FI Vette. My 61 with the 315/283 FI and 4.11 was amazing at a flat 20 MPG at freeway and above speeds. Even better than the 62.

 

I had no idea the old Rochester fuelie units made that much of a difference on fuel comsumption.
It's always a good day when I learn something new