Malfunctioning vacuum advance?

[MarcD]

I'm probably screwing this up right proper but my tests are telling me the vac advance is not working. Painted my timing ball bright orange and I have a perfect steady ball at 1500 rpm on a warm engine with the vacuum advance line disconnected.. Here is the problem, I have to advance my timing light (innova 3568) to 10 degrees advance to see the ball. I reset my timing light and plugged in the vacuum advance from the carb. No change. Increase timing light to 10 degrees and bam, happy orange ball shows up again. The dizzy with the ball centered in the hole from the drivers side and set the number 1 plug wire centered on the rotor. It took a little turning of the distributor to smooth out the idle but no more than a few degrees. Smooth warm idle is somewhere around 900 to 1,000 rpm. 

 

The car seems happy as best as I can tell. I don't notice any knocking. Pulls smooth through the full rev range. Cold starts are a non issue and hot starts are nearly instantaneous. I'm tempted to just leave it and drive the car while I look for a replacement or donor to rebuild. 

 

Is there another test for the vacuum diaphragm that I'm missing? Does it even matter if the car is happy? 

 

 

Edited November 21, 2022 by MarcD

['76mintgrün'02]

1 hour ago, MarcD said:

I reset my timing light and plugged in the vacuum advance from the carb. No change.

 

Are you running the vacuum line to ported or manifold vacuum?  If ported, there isn't enough vacuum at idle to make any change.  If you have it plugged into manifold vacuum, it should pull in around 12 degrees of advance at idle.

 

That's one way to test the pod.  Plug it into manifold vacuum and see if the timing marks move (and by how much).

 

You can also try sucking on the vacuum line and watching to see if you can move the points plate.  Sometimes the diaphragm leaks and you will be able to detect that by sucking on it.

 

Vacuum advance and retard distributors have double points plates and the upper portion gets moved by the pod.  Sometimes they get stuck together and the pod cannot move it.  If that's the case, the pod might still be good, even though it isn't able to give advance.  

 

Distributors require routine maintenance, or they'll wear out due to neglect.  The fact that your timing mark is steady is a good sign.  Checking/cleaning/lubricating the points plates is part of the maintenance process.  Keep grease on the center post cam too, so the points rubbing block doesn't wear it out.  Pull the felt plug out of the top and put a couple drips of oil in the center post too, while you're at it.

 

Which model distributor do you have?

[Mike Self]

Easy way to check your vacuum advance:  

 

1.  Pull the distributor cap and rotor

2. Disconnect the vacuum line at the carburetor end

3. suck on the vacuum hose, and observe the little rod that connects the vacuum capsule with the point plate

4. if the point plate moves--and it won't move very much--then the vacuum advance is functioning (i.e. it's working mechanically, but not necessarily with the correct timing).  If the point plate doesn't move at all, and you feel no resistance when you suck, then the vacuum diaphragm is torn and will need to be replaced.  

 

Once you know its functioning mechanically, then you can proceed with setting the timing. 

 

mike

[John76]

15 hours ago, MarcD said:

I have to advance my timing light (innova 3568) to 10 degrees advance to see the ball. I reset my timing light and plugged in the vacuum advance from the carb.

What is the advance setting on your light when you see the perfect orange ball at 1500rpm?

What is the rpm when you have to advance your light to 10 degrees to see the ball?

Your smooth idle at 900-1000rpm might indicate 15 degrees advance, so adding 10 degrees to your light will show the ball.

Check to see which direction the points plate moves when you do the "suck test" recommended by Tom and Mike.

You might have a vacuum retard distributor; in which case the points will move clockwise with vacuum. 

Also check the port(s) on your carb. Some have manifold vacuum AND ported vac. nipples. Test to determine what type you are connecting to your distributor. 

The Innova 3568 is a great timing tool!  Consider adding a vacuum gauge to your toolbox to fine-tune your carb.

 

John

 

[MarcD]

7 hours ago, John76 said:

What is the advance setting on your light when you see the perfect orange ball at 1500rpm?

10 degrees advance.

 

Here are my steps

-Set the #1 wire on the rotor with the ball centered in window.

-Let the car come up to temp to fully open the choke

-Set my light to zero advance and brought the RPM up to 1500 (No visible ball)

-Advanced the timing on the light until the ball came into view. Rock steady at 10 degrees

 

I think where I went wrong was trying to time off the ball mark at too low of an RPM. I put a vacuum pump on the advance and it seems to work as it should so tomorrow when I get some free time I'll start back from zero. I suppose it possible the diaphragm is far enough out of spec to loose vacuum pressure. I was able to find an FSM on this site so I downloaded the entire thing for reference. 

 

I've been driving the car a lot and I don't notice any detonation at hot idle or under full throttle. 

[Son of Marty]

I think you are reading the ball as tdc.

[MarcD]

On 11/21/2022 at 10:00 PM, Son of Marty said:

I think you are reading the ball as tdc.

 

The ball is 25 degrees advance, right? 

 

Maybe my logic is flawed. With the vacuum advance disconnected, if the ball is 25 degrees advance and I have to advance my light 10 degrees to bring the ball into view then I'm -10 degrees advance off the ball at idle. 

 

I tested the vacuum advance with a pump and it appears to work. Next I need to figure out how much advance the vacuum adds at idle speed. 

Edited November 24, 2022 by MarcD
clarification

[jimk]

1 hour ago, MarcD said:

Next I need to figure out how much advance the vacuum adds at idle speed.

None if the vacuum tube is connected to the correct nipple on the carb.

['76mintgrün'02]

46 minutes ago, MarcD said:

The ball is 25 degrees advance, right? 

 

Maybe my logic is flawed. With the vacuum advance disconnected, if the ball is 25 degrees advance and I have to advance my light 10 degrees to bring the ball into view then I'm -10 degrees advance at idle. 

 

I tested the vacuum advance with a pump and it appears to work. Next I need to figure out how much advance the vacuum adds at idle speed. 

 

Right, the ball is at 25 degrees.

 

If (the ball is 25 degrees advance and) you have to advance your light 10 degrees to bring the ball into view then you're 25 - 10= 15 degrees advance at idle... as John suggested.

 

On 11/21/2022 at 10:52 AM, John76 said:

Your smooth idle at 900-1000rpm might indicate 15 degrees advance, so adding 10 degrees to your light will show the ball.

 

There is an line on the flywheel for top dead center and it is usually marked OT.  It helps to mark that one with paint too, to make it easy to see under the light.  To confirm the math in the paragraph above, you'd just bump the timing up on the light, until the OT mark lines up with the driver's side of the oval hole and that will indicate your advance at idle.

 

Then, you can connect the advance pod and see if/how much the mark moves, by bumping the advance up on the light until the mark is aligned again.

 

On 11/20/2022 at 8:09 PM, '76mintgrün'02 said:

Are you running the vacuum line to ported or manifold vacuum? 

 

I'm guessing ported, since 15 degrees at idle is plenty and 27 would be way too much.  Pods typically pull in around 12 degrees and manifold vacuum will do that at idle.  As Jimk suggests, ported shouldn't add any.

 

1 minute ago, jimk said:

None if the vacuum tube is connected to the correct nipple on the carb.

 

The Ported vs. Manifold vacuum question often turns into an argument, but I think the answer depends on what the distributor has to offer.  I use ported vacuum with mine.  I think John76 prefers manifold on his, but we're still friends.

 

On 11/20/2022 at 8:09 PM, '76mintgrün'02 said:

Which model distributor do you have?

 

How much total-advance do you have with your current setting?  At what rpm does the distributor stop giving more advance? (all-in)  At what rpm does it start giving advance?  Are you using points, or something electronic?  If points, do you have a dwell meter to set them?

 

I have vacuum advance plumbed into ported vacuum and it does not ad any advance at idle, except fast idle while it is warming up.  I have one of the smog-equipment vacuum switches plumbed inline between the source and the pod, so I can turn it off from the driver's seat with the flip of a switch and turning it off during warm up definitely has a negative effect.  I have done the same sort of test while driving and it tells me that vacuum advance is a good thing.  There is a noticeable dip if I flip if off at light throttle cruise. 

 

Tom

[jimk]

3 minutes ago, '76mintgrün'02 said:

The Ported vs. Manifold vacuum question often turns into an argument, but I think the answer depends on what the distributor has to offer. 

If it's a weber carb, the weber tuning manual describes when and what causes the vacuum to appear in the tube/dashpot.  And there is only one nipple on the carb that is correct.

There is no idle advance setting, only the advance @ rpm for the 25 deg.  You get what you get at idle.

[Buckeye]

There are some variables that effects vacuum advance.  For example on 1976 49- states, vacuum advance is engaged only during start-up/ warm up if advance dashpot is present. So it may help us if you provide critical specs (i,e. model year, dizzy part #, dashpot present or not, etc.)

['76mintgrün'02]

Hi, Buckeye!  Where have you been?  Thank you for adding that.  That's sort of what I was getting at, when I said that selecting a vacuum source may depend on what the distributor has to offer.  These distributors were designed to work as part of the emissions package, so it may not be as simple as we'd like, trying to figure out how to make them work for us.

In a previous discussion about P vs M vacuum, it occurred to me that I might have been able to make manifold vacuum work for me, if I hadn't gone through the work of making my distributor give less total advance.

 

As these distributors wear, they tend to give more advance, as opposed to less.  So, if you need to keep the total advance low enough (by rotating the distributor), you may not have enough left at idle.  That's where using manifold vacuum might come in handy, because it will pull in more vacuum at idle.  Instead, I reduced the total advance given by the weights/springs, so I would have enough at idle while using ported vacuum.

 

 

44 minutes ago, jimk said:

If it's a weber carb, the weber tuning manual describes when and what causes the vacuum to appear in the tube/dashpot. 

 

I wonder if it is the same as what the ported nipple provides on the original Solex carb?  I also wonder if there were changes made between the years/models that the two-barrel Solex was made.  Is the CA Solex identical to the others?  I'd guess yes... and don't need to know, since I'm using a Weber 32-36, but I wonder how many things I don't know enough to wonder about.

 

The title of this thread mentions malfunctioning vacuum pods.  I have one that had a bad diaphragm, so I drilled it out and added an adjustment screw to be able to add/subtract advance without loosening/rotating the distributor.  That sure was fun.  (Sharing it is fun too).

 

 

 

So, malfunctioning pods aren't necessarily garbage.  

 

Tom

[jimk]

What happened to the wing nut?  I thought that was cool. 😃

['76mintgrün'02]

10 minutes ago, jimk said:

What happened to the wing nut?

 

I made a few different nuts and figured I'd mix it up a bit when adding a photo to this thread.  

 

 

The exposed screw end is "fake" and has been drilled and tapped for 6-32 threads.

 

 

 

 

I also made one using a Subaru wing nut, so it matches the ones on my air cleaner.

 

 

 

The exposed screw is fake on that one too.

 

 

The wing nuts make it easy to keep track of the advance changes, since one full rotation equals two degrees at the distributor, which is four degrees on the timing light (using 6-32 threads).  So, one quarter-turn per degree of advance.  But, there's no more vacuum advance, so I don't use the adjustable pod I made.  It's just for show'n'tell.  

 

Tom

[jimk]

2 hours ago, '76mintgrün'02 said:

I wonder if it is the same as what the ported nipple provides on the original Solex carb?

They will be in the ball park as to the same place above the rising edge of the throttle plate.

 

At closed throttle the air pressure at the port in the carb throat is the same as the pressure in the throat.  When the throttle plate opens enough the air rushing past it's edge reduces and if the throttle edge is near the port, the port pressure lowers and the vacuum pod begins to tug at the points plate.  Increased throttle opening angle causes the port pressure do depress more until at some throttle opening angle the port pressure increases to equal the pressure in the throat and vacuum advance goes away with increasing engine power.

 

2 hours ago, '76mintgrün'02 said:

As these distributors wear, they tend to give more advance, as opposed to less.  So, if you need to keep the total advance low enough (by rotating the distributor), you may not have enough left at idle.

Yes and is the reason BMW prescribed setting the idle to 25 deg @ at some rpm in the range where the dreaded detonation occurs.  And then the time of the spark would not be the cause of detonation.  Worn or new distributor, it will always not be the detonation cause.  Maximum mechanical advance will always be obtained it the distributor is not so far gone that it's ready for retirement.

 

As far as advance at idle, there is no correct number.  It can be anywhere between 0 and 15 degrees and the thing will idle, maybe not the best sounding.

 

The Germans were smart to select their method, even if it seems like a pain in the butt.