1949-1953 Loadamatic Distributor

[BUBBAS IGNITION]

We dont do a lot of stock loadamatics but for some reason i have done three this week for flathead customers etc. After shipping over 750 of our Chevrolet mechanical advance units i guess we become pretty one sided?
But i feel as if this orginal vacuum only unit is still very much understood so heres some verbage for discussion and a few pictures of the rebuild done this morning......

Motors manual calls this unit a " Holley Full Vacuum type " unit as it only has vacuum advance with No centrifical advance at all .
This vacuum advance is regulated entirely by the vacuum differential at the carburetor. Some call this venturi as the vacuum is developed when the throttle is opened and air flows thru the carb venturis. At idle this signal would be zero and wide open throttle it may reach 3-4 inches of vacuum ( pretty low strength signal).
The actual specs for the unit is 1 degree of engine timing at .30 ( 1/3 or one inch ) of vacuum and 22 degrees of engine timing at 3.7-4 inches of vacuum.
The slightest variation of the throttle plate will cause this signal to change quite a bit. Even a idle set screw adjustment will change the advance rates for the vacuum diaphram. Ford used this type unit from 1949 untill sometime in the 60s with great sucess as long as the engine was in good shape and properly adjusted..
Tear down is pretty easy , however the drive gear and spacer is a bear to remove as the roll pins are pressed into place!!!!
Once apart and cleaned inspect all parts and reassemble applying lube to all moving parts. Pay attention to the snap ring holding the breaker plate, the rotor retaining clip and bushing conditions.
The springs used for the calibration are mounted on twin adjustable pins. Adjustment is possible by pumping up the vacuum chamber however its pretty hard to adjust with vacuum settings so low...

[36tbird]

Bubba, can you please show a picture of the trash receptacle that these should go into?

[BUBBAS IGNITION]

Originally Posted by 36tbird

Bubba, can you please show a picture of the trash receptacle that these should go into?

That's good, really good!

[bk53]

thanks Bubba, always enjoy reading your posts.

Bill

[1937pickup]

If they were as bad as everyone says-why would Ford use them for so long?

[Step-down]

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Bubba always enjoy your post .

[BUBBAS IGNITION]

Actually they do great job for many,many miles.....as long as the carb and engine is in good shape and properly adjusted....

[Straightpipes]

Thanks Bubba, rarely does anybody take the time to explain these distributors. You truely do work on anything that makes a spark. I am running two flatheads. One with your Chebbie conversion and another with a mallory dual point that you reworked.
Quite a few guys attempt to run the stock distributor with dual carbs. I think that it is pretty much imposible. What are the thoughts on vacuum distributors with multiple carburators?

[49r]

I've never had any problem with them. Currently trying a Mallory dual point with 6 volt just to see what it would be like, but haven't noticed any improvement in performance or economy. It's centrifuagal advance only. Will put the Loadamatic back at some point - I like the original look.

[Frank Miller]

I went to a chevy conversion on my stock 49. Have not had a chance to really try it out. I am running the vacuum advance as well. As I understand it it will retard the timing a few degrees when stepping on the accelerator to prevent pinging allowing a little more advance at cruising speeds. Similar to how your wipers stop working when you stomp on it. What I do end up with is a little more advance at idle.
Bubba, What is the total advance of the chevy distributor and how much is centrifugal and how much is vacuum?

[BUBBAS IGNITION]

Originally Posted by Straightpipes

Thanks Bubba, rarely does anybody take the time to explain these distributors. You truely do work on anything that makes a spark. I am running two flatheads. One with your Chebbie conversion and another with a mallory dual point that you reworked.
Quite a few guys attempt to run the stock distributor with dual carbs. I think that it is pretty much imposible. What are the thoughts on vacuum distributors with multiple carburators?

Once you change the carbs the loadamatic is pretty much history. Maybe not impossible but pretty hard to even start to get it set up correct.

[BUBBAS IGNITION]

Originally Posted by Frank Miller

I went to a chevy conversion on my stock 49. Have not had a chance to really try it out. I am running the vacuum advance as well. As I understand it it will retard the timing a few degrees when stepping on the accelerator to prevent pinging allowing a little more advance at cruising speeds. Similar to how your wipers stop working when you stomp on it. What I do end up with is a little more advance at idle.
Bubba, What is the total advance of the chevy distributor and how much is centrifugal and how much is vacuum?

Centrifugal is 16 to 24 degrees and vacuum is 14 degrees on a stock setup. May vary a little.
The issue is that the vac and centrifugal overlap each other as you couldn't have full vacuum at wot or full centrifugal at idle. So combined they would provide a constant 15-24 degrees all the time after the engine was started.

[JT FORD]

I ran dual carbs with a load a matic for 60,000 miles with no problems. Had a dual point conversion with a Mallory coil and condensor............In l955 no one used anything off a Cheve...........

[rotorwrench]

I haven't messed with an 8BA carb for many moons but I have worked on several of the Holley 885 carbs for the Mercury cars. In the early 49 units it was set up for the vacuum advance pretty much like the 8BA carbs were. It was designed to give venturi vacuum from a specific port in one of the venturis plus vacuum from a port lower down by the throttle plate. The internal passage would leak some vacuum from the lower port when the throttle was opened condiderably. In mid 1950 they added a nylon ball in there to act as a check valve and close tha lower throttle port during high openenings of the throttle in order to make the system function more efficiently for wide open throttle and heavy throttle opening. Since Holley made both the carburetor and the distributor, they had a pretty good deal going with FOMoCo for a long time. It functions pretty well for a stock engine but became less efficient when the horse power ratings started to climb with MEL & FE block engines and the Y-blocks changed over to the small block Fords of the 60s. It just didn't do as well with the OHV engines but for flatheads it was adequate.

[BUBBAS IGNITION]

Good addition to the post! Have ya got any pictures of the passages etc to go with this discussion?
Maybe a running engine with a large vacuum gauge hooked to a manifold port and a carb Venturi port . Anyone ?.....?..

Originally Posted by rotorwrench

I haven't messed with an 8BA carb for many moons but I have worked on several of the Holley 885 carbs for the Mercury cars. In the early 49 units it was set up for the vacuum advance pretty much like the 8BA carbs were. It was designed to give venturi vacuum from a specific port in one of the venturis plus vacuum from a port lower down by the throttle plate. The internal passage would leak some vacuum from the lower port when the throttle was opened condiderably. In mid 1950 they added a nylon ball in there to act as a check valve and close tha lower throttle port during high openenings of the throttle in order to make the system function more efficiently for wide open throttle and heavy throttle opening. Since Holley made both the carburetor and the distributor, they had a pretty good deal going with FOMoCo for a long time. It functions pretty well for a stock engine but became less efficient when the horse power ratings started to climb with MEL & FE block engines and the Y-blocks changed over to the small block Fords of the 60s. It just didn't do as well with the OHV engines but for flatheads it was adequate.

[40 Deluxe]

Motor, Chilton's etc. Manuals of the early and mid-50's had cutaway diagrams of the carb passages that supplied vacuum to the Load-a-Matic distributor. As I remember, it was a mix of ported and venturii vacuum (ported vacuum goes away under heavy load/full throttle so venturii vacuum is needed to maintain the necessary advance). As air rushes through the venturii (which is a smaller diameter than the throttle bore) it causes a low pressure area (or partial vacuum) which allows atmospheric pressure in the float bowl to push the gas through the jets into the airstream. This partial vacuum is used to provide the high speed advance signal. Somewhere after '49 a 'spark valve' was added to the carb to further refine the advance curve. This is the thing that looks like an external power valve, sort of.
Incidentally, venturii vacuum is what Holley uses to open the secondaries on their 4 barrel carbs.

[richard rink]

I am running dual 94's on an 8CM, getting a vacuum signal off one of the carbs. I appreciate that the signal is diminished because of the dual set-up. To amplify the effect of the reduced vacuum, I removed the two springs on the breaker plate and installed a single, weaker spring. A small amount of suction causes rotation of the plate. In operation, with a heavy foot on the accelerator, there is sufficient advance to cause "pinging." Acceleration is excellent. This is very much a shade tree kind of approach, but I am satisfied that the set-up works. .

[rotorwrench]

Originally Posted by BUBBAS IGNITION

Good addition to the post! Have ya got any pictures of the passages etc to go with this discussion?
Maybe a running engine with a large vacuum gauge hooked to a manifold port and a carb Venturi port . Anyone ?.....?..

I'll see if this will work. You may have to open it in a new window and resize to read it.

The Lincoln 337 used a different system so the carb was set up differently.

[BUBBAS IGNITION]

Originally Posted by richard rink

I am running dual 94's on an 8CM, getting a vacuum signal off one of the carbs. I appreciate that the signal is diminished because of the dual set-up. To amplify the effect of the reduced vacuum, I removed the two springs on the breaker plate and installed a single, weaker spring. A small amount of suction causes rotation of the plate. In operation, with a heavy foot on the accelerator, there is sufficient advance to cause "pinging." Acceleration is excellent. This is very much a shade tree kind of approach, but I am satisfied that the set-up works. .

Good thinking Richard, that's what makes it work!

[BUBBAS IGNITION]

Originally Posted by rotorwrench

I'll see if this will work. You may have to open it in a new window and resize to read it.

The Lincoln 337 used a different system so the carb was set up differently.

Good pictures of the function and overall importance of the throttle opening and the adjustment required.
You can see that even a mis set idle speed would also effect spark timing....