1975 Distributor Advice - Swap from Vacuum Retard to Vacuum Advance

4Cruisers

Supporting Vendor
SILVER Star
Joined
Apr 2, 2015
Messages
6,972
^^^ This.

The 19100-61080 is what is often referred to as an extra small cap distributor - the 1/75 through 9/77 2F distributors have a larger diameter breaker plate and your existing Pertronix will not fit.
 
Joined
Dec 13, 2012
Messages
1,548
Location
KY
You do realize that switching from vacuum retard to vacuum advance means you have to switch where you pick up your vacuum source. Vacuum retard uses ported vacuum where vacuum advance needs direct vacuum.

So Motor Trend is wrong, what about City Racer? Here is what he has to say about a factory vacuum advance distributor he sells: "Due to vacuum advance, the distributor requires a vacuum source from the base of the carburetor." Base of the carburetor is manifold vacuum not ported.

What do the factory service manuals have to say as to the vacuum source for FJ40's that came equipped with vacuum advance distributors? And since we are talking de-smoged engines it should be a model that didn't come equipped with smog equipment from the factory.
 

brian

SILVER Star
Joined
Feb 7, 2003
Messages
11,275
Location
lebanon,pa
Website
www.facebook.com
Last edited:

4Cruisers

Supporting Vendor
SILVER Star
Joined
Apr 2, 2015
Messages
6,972
Ported vacuum for distributor vacuum advance on the Land Cruiser carburetors is adjacent to the idle mixture screw. On my stock '76 FJ40 with FJ60 electronic ignition, I used the EGR port for distributor vacuum advance, the port is located pretty much at the same location as the advance port on the later Land Cruiser carburetors that came on vehicles equipped with vacuum advance - '77s and later had vacuum advance, '78s had advance plus retard, '79s through '87s had vacuum advance plus additional advance for high altitude compensation.
 
Joined
Dec 13, 2012
Messages
1,548
Location
KY
I think part of the problem is the mismatch of parts. By this I mean carburetors and distributors designed to run under emission controls and then de-smog the engine without making adjustments to these parts or replacing them with parts designed to run without emission controls. Truly understanding the functional difference between ported or timed vacuum and manifold vacuum.

I think this article, written by a retired GM/Chrysler Engineer, does a good job of explaining how these various components work together. Even companies like Edelbrock provide ports on their carburetors for ported/emission controlled motors and manifold vacuum for non-emission controlled motors.

1406_edelbrock[1].jpg


You're free to feel or believe as you wish. I'm simply trying to make sure you have as much information as you need to make your decisions. Not trying to get in any pissing contests.
 

brian

SILVER Star
Joined
Feb 7, 2003
Messages
11,275
Location
lebanon,pa
Website
www.facebook.com
I think part of the problem is the mismatch of parts. By this I mean carburetors and distributors designed to run under emission controls and then de-smog the engine without making adjustments to these parts or replacing them with parts designed to run without emission controls. Truly understanding the functional difference between ported or timed vacuum and manifold vacuum.

I think this article, written by a retired GM/Chrysler Engineer, does a good job of explaining how these various components work together. Even companies like Edelbrock provide ports on their carburetors for ported/emission controlled motors and manifold vacuum for non-emission controlled motors.

View attachment 2778742

You're free to feel or believe as you wish. I'm simply trying to make sure you have as much information as you need to make your decisions. Not trying to get in any pissing contests.
so i assume you have manifold vacuum to your dizzy?
 

C6H12O6

SILVER Star
Joined
Dec 23, 2004
Messages
2,002
Location
Beaverton, Oregon
So, if the carb base vacuum advance port is ported vacuum, and I have a '74 carb with no vacuum advance port/nipple, I should be able to use the ported vacuum off the vacuum port threaded into the manifold in front of the carb that formerly supplied vacuum to the VSV?

I have the same '75+ small cap advance distributor as the OP, but no vacuum source.
 

Pighead

Stop calling it an FJ
Joined
Aug 31, 2004
Messages
8,393
Location
Denverish
That's sorta what this thread is about and there is a difference of opinion.
I think, on a 74 your dizzy vacuum came from the VSV, and it was probably a vacuum retard. I have no idea when or how much vacuum the VSV gave to the dizzy.
So can you use manifold vacuum on a LandCruiser vacuum advance dizzy in an F type engine? I don't know. You could probably try it, might not hurt anything and the LandCruiser should let you know how it works pretty quickly.
Report back here
Edit: i had my 74 carb fitted with the ported vacuum nipple during a rebuild
 
Joined
Dec 13, 2012
Messages
1,548
Location
KY
so i assume you have manifold vacuum to your dizzy?
To be honest, I wasn't sure so had to go take a look. Mind you I have a built 350 CI Chevy, without any smog equipment, with HEI distributor and Edelbrock E-Street EFI with in-tank fuel pump and fuel return. My vacuum advance on the distributor is connected to the ported vacuum on the throttle-body. My fuel pressure regulator vacuum fitting is connected to the manifold vacuum fitting on the throttle-body. All factory HEI distributors were built and used on smog equipment engines. I tried going through my setup documents but could not find any reference as to which port was recommended. Because the engine originally had smog equipment, smog pump with air tubes and EGR the distributor was hooked up to ported vacuum. My assumption at this point was that when I removed the smog equipment and installed the EFI I kept the vacuum line connected to a ported source. Because the ECU monitors the normal EFI sensors and makes adjustments as needed I've never really had a reason to change anything.
 
Joined
May 3, 2009
Messages
1,013
So, if the carb base vacuum advance port is ported vacuum, and I have a '74 carb with no vacuum advance port/nipple, I should be able to use the ported vacuum off the vacuum port threaded into the manifold in front of the carb that formerly supplied vacuum to the VSV?

I have the same '75+ small cap advance distributor as the OP, but no vacuum source.
I don't think so as the "vacuum port threaded into the manifold" is, indeed, manifold vacuum designed for a vac. retard distributor. It retarded the timing at idle and slowly returned it to normal as the throttle was opened. In other words: The timing advanced as you accelerated. The '75 distributor will not have the correct mechanical advance curve to compensate for A) the rapidly diminishing advance as you accelerate and B) the lack of part throttle advance for the lean air/fuel mixture at highway cruise conditions. Maybe the distributor you're using just happens to (somehow) perfectly overlap the diminishing advance from using manifold vacuum for the advancer as you step on the throttle, with the increasing vacuum the distributor was designed to receive from ported vacuum at part throttle positions. That would be impressive.

I also should add something to what 4Cruisers said...

Just because you find a carb base with a nipple doesn't mean it will have ported vacuum. Some years had different iterations of bases depending on where the vehicle was sold in the USA. Some did not come with ported vacuum iirc. You can use the EGR port to some effect as a ported vacuum source but it does come in later as it draws vacuum from slightly higher up the throat of the carb.
 
Last edited:

C6H12O6

SILVER Star
Joined
Dec 23, 2004
Messages
2,002
Location
Beaverton, Oregon
I know what you're saying, but the vacuum just pulls on a diaphragm. Whether the vacuum retards or advances your timing has nothing to do with vacuum source, per se, but how the distributor is designed to react to the pull on its diaphragm. Your comment makes it sound like the vacuum itself is different for the two distributors, which I think is also still a bit unclear. I still haven't heard a great description of exactly how the ported and manifold vacuum are different. Not saying they aren't, but the difference is unclear.

Are there graphs posted somewhere that compare the amount of vacuum from different sources at different RPM? That would be very helpful in sorting this out. If the porting at various places changes the timing of the pull on the diaphragm, that is one thing, and it probably wouldn't hurt anything to experiment. If the porting through the carb base only attenuates the spikes in the vacuum pressure, that is different. Would pulling full manifold vacuum against the distributor diaphragm be enough to damage it? Probably not, but I would love more info before I hook it up. It probably wouldn't be hard to collect the data, and somebody here probably has access to the right hardware to log it in real-time while driving.

FWIW, I have the '74 carb with no vacuum port in the carb base. The Aisin carb gurus (@FJ40Jim, et al.) routinely add a nipple to the base that access the correct vacuum for a later vacuum advance distributor, but also recommend re-curving the distributor at the same time, if I remember correctly. I messaged with Jim a couple years ago about it, but didn't discuss these kinds of details. I've got the '75+ small cap advance distributor on the truck right now with the vacuum advance just capped off, and it runs pretty dang well with just the mechanical advance the weights provide, but you can definitely feel it run out of advance as the revs climb up.
 

4Cruisers

Supporting Vendor
SILVER Star
Joined
Apr 2, 2015
Messages
6,972
I know what you're saying, but the vacuum just pulls on a diaphragm. Whether the vacuum retards or advances your timing has nothing to do with vacuum source, per se, but how the distributor is designed to react to the pull on its diaphragm. Your comment makes it sound like the vacuum itself is different for the two distributors, which I think is also still a bit unclear. I still haven't heard a great description of exactly how the ported and manifold vacuum are different. Not saying they aren't, but the difference is unclear.

Are there graphs posted somewhere that compare the amount of vacuum from different sources at different RPM? That would be very helpful in sorting this out. If the porting at various places changes the timing of the pull on the diaphragm, that is one thing, and it probably wouldn't hurt anything to experiment. If the porting through the carb base only attenuates the spikes in the vacuum pressure, that is different. Would pulling full manifold vacuum against the distributor diaphragm be enough to damage it? Probably not, but I would love more info before I hook it up. It probably wouldn't be hard to collect the data, and somebody here probably has access to the right hardware to log it in real-time while driving.

FWIW, I have the '74 carb with no vacuum port in the carb base. The Aisin carb gurus (@FJ40Jim, et al.) routinely add a nipple to the base that access the correct vacuum for a later vacuum advance distributor, but also recommend re-curving the distributor at the same time, if I remember correctly. I messaged with Jim a couple years ago about it, but didn't discuss these kinds of details. I've got the '75+ small cap advance distributor on the truck right now with the vacuum advance just capped off, and it runs pretty dang well with just the mechanical advance the weights provide, but you can definitely feel it run out of advance as the revs climb up.
A recurve is only really needed for the 8/80 through 8/87 2F big cap distributors when used on the 8/80 through 8/87 2F engines that have been de-smogged (mainly the removal of the EGR system), due to the change to the cylinder head.

Changing the advancer on the 1/75 through 8/76 from retard to advance is just about as straightforward as it gets, pull out the old advancer and slip in the new, either with an 8/76 through 9/77 stock 2F advancer or an advancer from another non-Land Cruiser Toyota engine. I've sold a number of these, plus I've used them in quite a few 2F distributor refurbishments.

The ported vacuum on the carburetor doesn't kick in until the primary throttle valve opens beyond the hole in the carburetor throttle bore, therefore there is no distributor advance at idle. Once it's opened beyond the hole, the timing advance increases with engine vacuum. On the other hand, manifold vacuum would advance the distributor timing even at idle, when it's not needed.

At the distributor, the maximum vacuum advance is set in a couple of ways. On distributors through 8/80, there are two lock nuts on the actuator rod that can be adjusted to limit travel of the rod. I usually set mine to ~3.8mm, which roughly corresponds to 10 degree distributor advance, or 20 degrees engine advance. On the 8/80 through 8/87 advancers, the internal design features limit the actuator J-arm travel. I haven't cut one apart to see the internals, but I know that @NeverGiveUpYota has, and has posted photos.
 
Last edited:

brian

SILVER Star
Joined
Feb 7, 2003
Messages
11,275
Location
lebanon,pa
Website
www.facebook.com
At the distributor, the maximum vacuum advance is set in a couple of ways. On distributors through 8/80, there are two lock nuts on the actuator rod that can be adjusted to limit travel of the rod. I usually set mine to ~3.8mm, which roughly corresponds to 10 degree distributor advance, or 20 degrees engine advance. On the 8/80 through 8/87 advancers, the internal design features limit the actuator J-arm travel. I haven't cut one apart to see the internals, but I know that @NeverGiveUpYota has, and has posted photos.
which end is that 3.8~mm from? the end of the threads, or the flat of the vac pot housing?

20210911_094446.jpg
 

4Cruisers

Supporting Vendor
SILVER Star
Joined
Apr 2, 2015
Messages
6,972
which end is that 3.8~mm from? the end of the threads, or the flat of the vac pot housing?

View attachment 2783237
Between the nuts and the flat of the vac pot housing. Given a distance of 22mm between the centerline of the distributor shaft and the centerline of the stud on the breaker plate, using a right triangle calculator, a travel of 3.8mm rotates the breaker plate approximately 9.95 degrees.
 

brian

SILVER Star
Joined
Feb 7, 2003
Messages
11,275
Location
lebanon,pa
Website
www.facebook.com
Between the nuts and the flat of the vac pot housing. Given a distance of 22mm between the centerline of the distributor shaft and the centerline of the stud on the breaker plate, using a right triangle calculator, a travel of 3.8mm rotates the breaker plate approximately 9.95 degrees.
that would be the logical answer, just wanted to certain...thanks.
 
Joined
Jan 6, 2003
Messages
1,017
I know what you're saying, but the vacuum just pulls on a diaphragm. Whether the vacuum retards or advances your timing has nothing to do with vacuum source, per se, but how the distributor is designed to react to the pull on its diaphragm. Your comment makes it sound like the vacuum itself is different for the two distributors, which I think is also still a bit unclear. I still haven't heard a great description of exactly how the ported and manifold vacuum are different. Not saying they aren't, but the difference is unclear.

Are there graphs posted somewhere that compare the amount of vacuum from different sources at different RPM? That would be very helpful in sorting this out. If the porting at various places changes the timing of the pull on the diaphragm, that is one thing, and it probably wouldn't hurt anything to experiment. If the porting through the carb base only attenuates the spikes in the vacuum pressure, that is different. Would pulling full manifold vacuum against the distributor diaphragm be enough to damage it? Probably not, but I would love more info before I hook it up. It probably wouldn't be hard to collect the data, and somebody here probably has access to the right hardware to log it in real-time while driving.

FWIW, I have the '74 carb with no vacuum port in the carb base. The Aisin carb gurus (@FJ40Jim, et al.) routinely add a nipple to the base that access the correct vacuum for a later vacuum advance distributor, but also recommend re-curving the distributor at the same time, if I remember correctly. I messaged with Jim a couple years ago about it, but didn't discuss these kinds of details. I've got the '75+ small cap advance distributor on the truck right now with the vacuum advance just capped off, and it runs pretty dang well with just the mechanical advance the weights provide, but you can definitely feel it run out of advance as the revs climb up.
I posted some vaccuum curves a long time ago, but they were for a later model big cap distributor. This was a static test so not really applicable to anything in real life other that to satisfy my curiosity. I had always thought about re-testing with sensors logging the vacuum readings in real time while driving, but I'll probably never get around to doing it now.


Difference between ported and manifold was mostly at idle/low RPM. I think I ran with the dizzy connected to manifold vacuum for a while, I don't really remember the outcome. I don't think I noticed much of a difference, and since I had already drilled the carb for ported vacuum (pics in another thread) so I just ran with ported. Ported and manifold essentially become the same after a certain point, so you won't damage anything testing.
 

Users who are viewing this thread

Top Bottom