Dizzy vacuum can ID

[grandfatherjim]

I've been swapping two distributors back and forth and now can't recall if I also swapped vacuum cans between them in the process. (It's been about a two year process.)
I don't see any numbers on the vacuum cans, but one has a "flat topped outward bump" in the centre, and one has the outward bump with a dimple in it like so:

http://homepage.mac.com/ratwell/.Pictur ... 7-SVDA.jpg

The two distributors in question are a 205E and a 205AB.

Anyone know?
TIA,
Jim

[Amskeptic]

I've been swapping two distributors back and forth and now can't recall if I also swapped vacuum cans between them in the process. (It's been about a two year process.)
I don't see any numbers on the vacuum cans, but one has a "flat topped outward bump" in the centre, and one has the outward bump with a dimple in it like so:

http://homepage.mac.com/ratwell/.Pictur ... 7-SVDA.jpg

The two distributors in question are a 205E and a 205AB.

Anyone know?
TIA,
Jim

It would help to start with your model year and engine and any modifications/changes to the original equipment. As I remember (and that is pushing it right there), you have a dual carb bus that should have a vacuum advanceANDretard distributor.

The external configuration of the can is next to useless as a determinant of what you ought to have. Distributor numbers can come with different cans depending on original application. When I am dealing with a mystery distributor, I merely attempt to catch the signposts on the advance curve with a timing gun.
Centrifugal: 25-28* @ 3,200 rpm, starts at about 1,200 rpm, hits 16* or so by 2,200 rpm.
Vacuum Advance: hits 36-40* on throttle blip.
Vacuum Retard: pulls timing down by 10-12* from wherever your idle timing is on centrifugal.

Vacuum modification to the timing curve is in the service of the carburetion. The retard is to work with the central idling circuit or airflow of the FI throttle body. The advance is just to help with economy and transitions, it generally works across a broad array of carburetors/fuel injection systems, the variations in the range allowed by the vacuum unit have more to do with the presence/rpm of the vacuum signal itself.
You can modify vacuum advance/retard range by judicious applications of bending to the limit post and filing the arm where necessary . . . carefully.
Colin

[grandfatherjim]

I've been swapping two distributors back and forth and now can't recall if I also swapped vacuum cans between them in the process. (It's been about a two year process.)
I don't see any numbers on the vacuum cans, but one has a "flat topped outward bump" in the centre, and one has the outward bump with a dimple in it like so:

http://homepage.mac.com/ratwell/.Pictur ... 7-SVDA.jpg

The two distributors in question are a 205E and a 205AB.

Anyone know?
TIA,
Jim

It would help to start with your model year and engine and any modifications/changes to the original equipment. As I remember (and that is pushing it right there), you have a dual carb bus that should have a vacuum advanceANDretard distributor.

The external configuration of the can is next to useless as a determinant of what you ought to have. Distributor numbers can come with different cans depending on original application. When I am dealing with a mystery distributor, I merely attempt to catch the signposts on the advance curve with a timing gun.
Centrifugal: 25-28* @ 3,200 rpm, starts at about 1,200 rpm, hits 16* or so by 2,200 rpm.
Vacuum Advance: hits 36-40* on throttle blip.
Vacuum Retard: pulls timing down by 10-12* from wherever your idle timing is on centrifugal.

Vacuum modification to the timing curve is in the service of the carburetion. The retard is to work with the central idling circuit or airflow of the FI throttle body. The advance is just to help with economy and transitions, it generally works across a broad array of carburetors/fuel injection systems, the variations in the range allowed by the vacuum unit have more to do with the presence/rpm of the vacuum signal itself.
You can modify vacuum advance/retard range by judicious applications of bending to the limit post and filing the arm where necessary . . . carefully.
Colin

Your memory is correct. Dual carb, '72 1700cc with both advance and retard on the distributor. Both cans have both.
We set advance to 28 (although you mentioned up to 32* is OK) at somewhat above 3000 rpm, which is what I'm still doing. Sometimes I go for 30, if it gives me amore sensible idle rpm.
Now, original distributor back in, performance is much improved, even with its flaws. However it's idling really high once warm.
Jim

[Amskeptic]

it's idling really high once warm.
Jim

Warm is where it lives. Perhaps it is actually idling really low when cold.

Does vacuum retard actually pull down idle? With warm engine, pull hose off. Idle should go up. Put hose back on. Idle should drop.

Culprits for no vacuum retard actuation can include:
leaky hose
leaky retard diaphragm
incorrectly set left throttle plate

[grandfatherjim]

it's idling really high once warm.
Jim

Warm is where it lives. Perhaps it is actually idling really low when cold.

Does vacuum retard actually pull down idle? With warm engine, pull hose off. Idle should go up. Put hose back on. Idle should drop.

Culprits for no vacuum retard actuation can include:
leaky hose
leaky retard diaphragm
incorrectly set left throttle plate

OK; got around to this. Sometimes things take a while here in Wally World.
So yup, pulling off advance hose with engine warm does indeed cause idle to go up.
Meanwhile, looking around online, it is next to impossible to see any correlation between physical attributes of the vacuum can and its year i.e. specs. However I did spot that the can's part number should be 07-101, according to this site:

http://www.oldvolkshome.com/ignition.htm#B1972

but cannot find said number anywhere on the can that is presently not on the engine (and which I suspect is the right one).

I could just swap, but would feel better understanding why the difference between hot and cold. I take your point that hot is where we want things performing properly, for starters.

[Amskeptic]

pulling off XadvanceX RETARD hose with engine warm does indeed cause idle to go up.

but cannot find said number anywhere on the can that is presently not on the engine (and which I suspect is the right one).

I could just swap, but would feel better understanding why the difference between hot and cold. I take your point that hot is where we want things performing properly, for starters.

Test for function. That is all that really matters in this world, 35 years after they had to split hairs to get past emissions.
Colin

[grandfatherjim]

pulling off XadvanceX RETARD hose with engine warm does indeed cause idle to go up.

but cannot find said number anywhere on the can that is presently not on the engine (and which I suspect is the right one).

I could just swap, but would feel better understanding why the difference between hot and cold. I take your point that hot is where we want things performing properly, for starters.

Test for function. That is all that really matters in this world, 35 years after they had to split hairs to get past emissions.
Colin

Whoops yes retard - I did the right thing but wrote the wrong thing. So I do have function.

I was thinking that different cans might have different amounts of rod movement for a given vacuum.

[Amskeptic]

pulling off XadvanceX RETARD hose with engine warm does indeed cause idle to go up.

but cannot find said number anywhere on the can that is presently not on the engine (and which I suspect is the right one).

I could just swap, but would feel better understanding why the difference between hot and cold. I take your point that hot is where we want things performing properly, for starters.

Test for function. That is all that really matters in this world, 35 years after they had to split hairs to get past emissions.
Colin

Whoops yes retard - I did the right thing but wrote the wrong thing. So I do have function.

I was thinking that different cans might have different amounts of rod movement for a given vacuum.

They really are not that sophisticated. They rely on the carb's signal, which is hard-engineered into the design of the carb. They are just a spring-loaded diaphragm with a discrete amount of movement . . . and we can adjust some of that movement, by the way.
Colin