Vacuum Advance making things work better... at idle?

[Scotty]

I have gone through a mess of things on this car. Electronic ignition gone and a new set of points, condenser, fine wire lead, wireset, distributor cap, coil, reset Weber with correct float, cleaning and validating working mechanical fuel pump and other things, and the car will start but rocks hard and runs well... like a tractor.

I start messing with the idle/mixture screws, but if I stop messing with the screws for the weber and adjust only the vacuum advance at idle, it suddenly wants to behave itself and run right and the idle speed/mixture screws start to resemble what they're supposed to be set at. What would cause the vacuum advance to do this at idle? Before the electronic ignition was put in, the car operated with a set of points that were spot on. That was changed because the points had gone bad and also because I didn't know how to work with them and was told I could drop in the electronic ignition and do nothing else and the car would be ok.

If I give it gas, the engine instantly wants to die but catches itself. It gets hot abit faster than normal.

The car is timed at 6 degrees BTDC. I will verify this today or tomorrow to make sure, but that's what it was set for on the paperwork and no one has touched the timing on this car. Like many other things I have never done this, so it'll be a learning experience.

Will adjusting vacuum advance blind or 'by ear' risk damaging the car?

As it stands, the car is getting plenty of gas and is operating as if its running very lean and popping through the carb. The Vacuum Advance was originally turned all the way in and 'off' as I understand it. If any of this is wrong, please tell me.

Thoughts?

 

[hartmandm]

Scotty,

I haven't had any coffee yet this morning, but I am wondering how you are adjusting the vacuum advance. If you are back to the stock Lucas 25D4 distributor setup, then the vacuum advance occurs via the assortment of weights internal to the distributor as they spin at higher RPMs. What knob, lever, or screw are you adjusting on which component to adjust the vacuum advance?

Mike

 

[belmateo]

Scotty,
The new car I bought was a 1974 mid year TR6 and it had the same problem you are describing. The cause was the plate in the distributor that the points mount to was not quite perpendicular to the shaft. What was happening is the dwell angle would change causing it to run rough and hesitate. Do you have any means of checking the dwell angle while this is happening?

 

[husky drvr]

I haven't had any coffee yet this morning, but I am wondering how you are adjusting the vacuum advance.

Mike,

Hope you've had an enjoyable coffee by now.

The swinging weights below the breaker plate is the centrifugal advance system and controls breaker plate position by engine speed. The diaphragm in the vacuum canister, with the "ported vacuum" from the carb port, pulls the spring attached to the top of the breaker plate to allow the addition of more ignition advance based on engine "load."

After decoding Scotty's descriptions for awhile, I think he is using the vernier adjustment on the vacuum canister to do his ignition adjustments, not having a clue where his ignition timing is actually set, only stating that his engine "runs better." What Scotty needs is a mentor, on site.

Have a good day,

 

[Scotty]

I am using the vernier to adjust advance at idle. I read on one of the forums that it should really set in the middle and the module is screwed all the way back into the distributor tightly. I didn't do this, this is how I got it.

I noticed that when the advance gets closer to the 'middle' line on the module that the car starts to want to run normal, albeit a lot stronger than it was with the electronic ignition.

I'm thinking that the electronic ignition was 'hiding' a lot of the problems I'm having by mapping out the timing. When it started to fail was when everything started coming apart. Just a random thought, I know there's a lot of things at play here.

Scotty,
The new car I bought was a 1974 mid year TR6 and it had the same problem you are describing. The cause was the plate in the distributor that the points mount to was not quite perpendicular to the shaft. What was happening is the dwell angle would change causing it to run rough and hesitate. Do you have any means of checking the dwell angle while this is happening?

I have a Multimeter that can be set to read dwell. I have to read up on how to set it up on the Alpine and read the numbers on the screen are degrees in decimals (ex: 63.0 is 63 percent). What's the best way to hook it up to the car? Red to Coil - and ground to ground?


I'm going to start from go and time the car myself with a timing light. Not touching any distributors or anything else, just want to see where it is now. And go from there.

 

[hartmandm]

I assumed Scotty was making adjustments via the vernier but wanted to hear from him. I thought the vernier provides for fine tuning of the static ignition timing, not the vacuum advance timing ...

Mike

 

[husky drvr]

I assumed Scotty was making adjustments via the vernier but wanted to hear from him. I thought the vernier provides for fine tuning of the static ignition timing, not the vacuum advance timing ...

Mike

Mike,

You're correct about the vernier and fine tuning of the static timing.

then the vacuum advance occurs via the assortment of weights internal to the distributor as they spin at higher RPMs.

I wouldn't have replied except for your implication about the flyweights being part of vacuum advance. They are not.

Two different systems, two different methods of applying the ignition advance, and the ignition advance of each system is additive - not one being part of the other.

Hope this helps,

 

[hartmandm]

Right. The spinning weights are the centrifugal advance. My bad.

 

[Scotty]

Hypothetical question: If I installed a new distributor, should the advance be set at its center line (the longest line) or should the module be all the way back against the distributor? Since I put points back in, I'd like to know what the base setting is on the marks on the vacuum advance.

 

[hartmandm]

Sounds like your vernier was in the fully retarded position and you were measuring 6 degrees of static timing at idle?

Set the vernier to its middle position. That allows you the option to perform fine tuning by advancing or retarding. Then set the static ignition timing by rotating the distributor. If you were at 6 degrees static before, I'd probably start with 8 degrees at idle. See how it is running then. Then with a known static ignition timing you can check if the centrifugal advance is working as expected. Don provided the centrifugal advance details from WSM 145 for an Alpine in his post in your other thread: https://forum.sunbeamalpine.org/index.php?threads/jerking-while-driving-and-stall.32954/post-243545

Disconnect the vacuum line from the distributor when checking how the centrifugal advance is behaving. Since the distributor is on the car, you will have to add the static timing to the centrifugal advance number given in WSM 145 to compare that total against what you are measuring. E.g. centrifugal advance at 2000 rpms is 15 to 19 degrees. If your static timing is 8 degrees, you should be seeing between 23 and 27 degrees using a timing light. You need an accurate tach or an accurate way to measure engine RPMs for this test.

When I checked my distributor's centrifugal advance, it was not advancing as it should. I then sent out the distributor for a rebuild. After rebuild, the rebuilder told me to set the static ignition timing to 12 to 15 degrees. He told me he had modified the centrifugal advance to align better with today's gasoline formulations. I followed his advice and the car ran well on premium gas (93 octane E10).

From WSM 145:
Timing adjustments
Two means of adjusting the ignition timing are provided.
They are:-
1. A clamp screw mounted horizontally. This is the coarse adjustment and when it is slackened the body of the distributor can be rotated in its mounting plate.
2. The vernier control. This provides an easy means of making small adjustments to the ignition timing to give the best performance from a particular fuel or to eliminate "pinking" when excessive carbon deposits have formed in the engine. One turn of the vernier knurled adjustment is
equivalent to three degrees of crankshaft rotation and one vernier adjustment spacing to four degrees of crankshaft rotation.
The knurled adjustment should be rotated clockwise to retard and anti-clockwise to advance as shown by the letters "R" (retard) and "A" (advance) cast on the distributor body close to the knurled adjustment.

Mike

 

[Scotty]

I took the plate out of the distributor and both springs seemed fine, no brittleness or aging, both are lightly greased and strong. Put it back together. I'm abit suspicious of the vacuum advance module itself because I had to do a little wrangling to move it on and off and it doesn't seem solid

Car fires up, engine runs like a tractor. Carb is getting gas from a mechanical pump that is working fine but the Carb reacts by running super lean to the point of backfiring. Anything past 1/4 choke kills it. I already checked the power valve in the top of the Carb and that and the rubber gasket for it are new and flat.

Bought a timing light and about to check timing myself. I read up on the basics and how to adjust the distributor to advance or retard. Not touching that until I find out exactly what the car's timing is set and set it to 6-10 degrees before tdc? Is this the correct way to go about this?

 

[Scotty]

Sounds like your vernier was in the fully retarded position and you were measuring 6 degrees of static timing at idle?

Set the vernier to its middle position. That allows you the option to perform fine tuning by advancing or retarding. Then set the static ignition timing by rotating the distributor. If you were at 6 degrees static before, I'd probably start with 8 degrees at idle. See how it is running then. Then with a known static ignition timing you can check if the centrifugal advance is working as expected. Don provided the centrifugal advance details from WSM 145 for an Alpine in his post in your other thread: https://forum.sunbeamalpine.org/index.php?threads/jerking-while-driving-and-stall.32954/post-243545

Disconnect the vacuum line from the distributor when checking how the centrifugal advance is behaving. Since the distributor is on the car, you will have to add the static timing to the centrifugal advance number given in WSM 145 to compare that total against what you are measuring. E.g. centrifugal advance at 2000 rpms is 15 to 19 degrees. If your static timing is 8 degrees, you should be seeing between 23 and 27 degrees using a timing light. You need an accurate tach or an accurate way to measure engine RPMs for this test.

When I checked my distributor's centrifugal advance, it was not advancing as it should. I then sent out the distributor for a rebuild. After rebuild, the rebuilder told me to set the static ignition timing to 12 to 15 degrees. He told me he had modified the centrifugal advance to align better with today's gasoline formulations. I followed his advice and the car ran well on premium gas (93 octane E10).

From WSM 145:
Timing adjustments
Two means of adjusting the ignition timing are provided.
They are:-
1. A clamp screw mounted horizontally. This is the coarse adjustment and when it is slackened the body of the distributor can be rotated in its mounting plate.
2. The vernier control. This provides an easy means of making small adjustments to the ignition timing to give the best performance from a particular fuel or to eliminate "pinking" when excessive carbon deposits have formed in the engine. One turn of the vernier knurled adjustment is
equivalent to three degrees of crankshaft rotation and one vernier adjustment spacing to four degrees of crankshaft rotation.
The knurled adjustment should be rotated clockwise to retard and anti-clockwise to advance as shown by the letters "R" (retard) and "A" (advance) cast on the distributor body close to the knurled adjustment.

Mike

Gotcha. Doing this tomorrow, will report then. Thank you!

 

[beamdream]

I am using the vernier to adjust advance at idle. I read on one of the forums that it should really set in the middle and the module is screwed all the way back into the distributor tightly. I didn't do this, this is how I got it.

I noticed that when the advance gets closer to the 'middle' line on the module that the car starts to want to run normal, albeit a lot stronger than it was with the electronic ignition.

I'm thinking that the electronic ignition was 'hiding' a lot of the problems I'm having by mapping out the timing. When it started to fail was when everything started coming apart. Just a random thought, I know there's a lot of things at play here.


I have a Multimeter that can be set to read dwell. I have to read up on how to set it up on the Alpine and read the numbers on the screen are degrees in decimals (ex: 63.0 is 63 percent). What's the best way to hook it up to the car? Red to Coil - and ground to ground?


I'm going to start from go and time the car myself with a timing light. Not touching any distributors or anything else, just want to see where it is now. And go from there.

Dwell is the period of time between closing and opening of the contact points, this can be adjusted by setting the contact points gap. Dwell is expressed in degrees; this relates to the rotation of the distributor rotor between spark plug leads in the distributor cap, in essence it's a measurement of how long the points are closed whilst the distributor rotates.

In the overall scheme of things, when you first set up the timing, this doesn't have a great impact on how the engine runs ; long story short, if the points are set to correct gap and are opening at the correct time, as far as the basic ignitioon settings are concerned, the engine will run. Not saying forget about dwell, but its something to deal with once you've got the timing sorted.

As to hooking up the meter, yes it's red to coil and the other to a good ground.

In all of this I'm assuming you're working wih a points distributor ??
Have to say it's hard to keep track of where you've been; dwell isn't something you can mess with if you're using electronic ignition.

 

[Rick Young]

Hi, When I was setting up my SV I adjusted the point gap until I had the correct dwell angle. Then I rotated the engine to line up the timing marks on the pulley and front cover. Set the vernier adjustment to the center and loosened the distributor to rotate it to statically time the engine as described in the WSM. The vernier adjuster allowed for small adjustments. It still was not right. I sent the distributor to Advance and was told i had rust under the breaker plate and a worn bush. The rebuilt distributor works perfectly.

 

[Shannon Boal]

I love seeing analytical minds at work! So when you rotate the adjustment it changes the time of the primary circuit opening. I think it changes the position of the rotor relative to the terminals in the cap. And it moves the points plate. And the idle quality changes in a manner unlike a simple change in spark timing. So, does the primary have a fault in the wire to the points, or the points plate ground wire to the distributor body? You could check for voltage drop from the points set to distributor body.....wiggle things, stuff like that. And, in the secondary ignition circuit, does it have faults from the rotor button position being wrong? The rotor arm gets close enough to the cap terminals for the spark to jump and connect to the proper spark plug. If it moves a little further away as you work the vacuum advance this could be happening here. Is this one of the rotors with a too short arm? (I see on the UK site they have found defective rotors out there.) Old time automotive electronic analyzers could measure that....those things are tricky to find.

 

[Scotty]

After decoding Scotty's descriptions for awhile, I think he is using the vernier adjustment on the vacuum canister to do his ignition adjustments, not having a clue where his ignition timing is actually set, only stating that his engine "runs better." What Scotty needs is a mentor, on site.

Have a good day,

What I need is to slow down, clear my head and do things in steps. I keep getting in my own way lol.

And fwiw, what I thought the original timing of the car was set at, was actually what it was set at. Found the paperwork for it. But I got to learn how to do all of that thanks to the threads on the board and my dumb questions. Happy about that .