Spark Control Valve?

[wallaka]

Am I crazy or should there be one here? The white looking line is the vac line to the distributor. When I rebuilt this carb, I hadn't found this forum yet. Reading here, it seems like something is missing.

Would the lack of an SCV cause the engine to be emasculated? It has no power at all really. It runs smoothly, no hesitation or bogging, but no power at all. I took the vacuum advance line off and sucked on it, and the plate inside the distributor moved, so that works. I am thinking that it just doesn't get the right signal.

 

[jahearne]

It doesn't look like it because it's not threaded. Is there a passage/hole into the carb body? Can't tell from the angle of the photo.

 

[wallaka]

I've seen the pics of the SCV, and there is nothing like this on the carb. That's the only passage that is open, so I guess that I either have a non-SCV carb, or it's missing. I'll go look at it more closely, be back in a minute.

Hmm. I can't see around the corner, but stuck a probe in there and it seems to be a dead end, or the hole is smaller than the probe is. I don't know.

 

[powerband]

This is a good question, The common 1904's used on most earlier engines didn't use the SCV valve but do provide a ported vacuum source (Venturi and Manifold vacuum) . What is the problem using Loadamatic distributor with non-scv dual ported carbs?.

PB 8)

http://home.comcast.net/~scottwickett/m ... /scv-1.jpg

 

[66 Fastback]

I'm no expert on the earlier carbs, but a ported source is just a vacuum port located right above and very close to the throttle plate. It provides little vacuum at idle with the throttle closed. It does not provide venturi vacuum. The vac source near the throttle plate shown in the diagram you attached is a ported vacuum source. Venturi vacuum is very low at idle because very little air is flowing through the venturi. As the throttle plate is openned and the engine rpm increases more air flow creates more vacuum allowing the Load-a-matic to increase the spark advance with engine speed.
Manifold vacuum has a port or pickup located below the throttle plate.
Keep in mind that for other throttle positions other than idle, manifold vacuum and ported vacuum are the same.
The SCV is a valve that switches vacuum source back and forth from the manifold vacuum to the venturi vacuum source. The SCV is calibrated to do this at a certain level of vacuum when the level of manifold vacuum decreases as the throttle plate is openned. The switch to venturi vac allows provides some vacuum to the distributor so that all of the ignition advance is not completely dropped.
Ported or manifold vacuum sources alone will not operate the Load-a-matic distributor properly. See the sticky at the top of this section.
If the Load-a-matic distributor is hooked to a carb that only has a manifold vac source OR a ported vac source, a "bog" will be created because as the throttle plates are openned quickly, the vacuum level decreases rapidly and all of the vacuum advanced ignition timing goes away. A distributor with centrifugal advance uses the engine rpm & the centrifugal weights to maintain some level of ignition advance as the engine accelerates.
Doug

 

[wallaka]

The car runs fine, doesn't bog or hesitate, no stubling or anything. From what I've read, if a venturi or manifold only vacuum signal won't give enough advance at high loads or high rpm--which could explain the lack of power... How can I tell if the distributor is a Loadamatic or a post-68 one? Just take the plate from the distributor and see if there are weights, or is there an easier way?

 

[66 Fastback]

Someone posted a way to distinguish the two by looking at them but I cannot remember who that was. I think you can see the weights below the plate and also the pivot pins that hold the weights. However, you could disconnect and plug the vaccum line and then rev the engine. Using your timing light, if it advances, it has centrifugal advance. If it does not advance, you either have a Load-a-matic or a centrifugal advance distributor that does not function properly.
Doug

 

[wallaka]

Didn't even think of that Well, that's what you guys are for, to pick up what I miss. I need to check the timing anyways, I never have.

 

[Mercury Mike]

That is the hole where the SCV goes on the holley 1940, though.

 

[CZLN6]

Howdy All:

The quick and dirty way to determine a Load-O-Matic (L-o-M) distributor is to remove the distributor cap and look for two advance return springs at the 5:00/6:00 position. One will be heavier and one lighter. If there are not advance return springs evident/or located under the point/stator plate you have a later distributor.

If you have a LoM distriburtor and a non-SCV carb you will be frustrated with smoothness and performance. You can cover up the problems some with more initial advance and a finely tuned carb, but it's only a cover-up.

What do you have your initial advance set at now?

Powerband- I have never seen a Holley #1904 that did not have a SCV. Please let me know where to look for a non/SCV #1904. A non/SCV 1904 would be an advantage for the end carbs on a tri-carb setup.

Adios, David

 

[pedal2themetal45]

OH MAN
YOU SAID
*********************************************************
It has no power at all
I need to check the timing anyways, I never have.

*********************************************************
If you have no power your timming is probubly way off
1. CHECK YOUR TIMMING
2. CHECK YOUR TIMMING
and
3. you havent pluged you choke heater tube hole in the choke housing there is a slight vacuum leak there for sure.
Tim

 

[wallaka]

Gotta wait for the timing light to get here, it's in my household goods en route from Germany. I know I need to check the timing, but when I bought the thing six years ago I shipped out a couple months later, never got the car running right. Anyways, that's definitely something to do. There seem to be a couple of little vacuum leaks like in the wiper switch (found that out yesterday).

David, I looked at the distributor and have two springs like you described. So this looks like a Loady, I guess that's part of my problem.

You guys are awesome. I guess I'll start looking for a DS2, a DUI is a little out of my price range.

 

[Mercury Mike]

Is that hole into the carb threaded or not? 'Cause if that's a 1940, then that's where the SCV goes. There should be one in a rebuild kit.

 

[powerband]

Howdy All:
Powerband- I have never seen a Holley #1904 that did not have a SCV. Please let me know where to look for a non/SCV #1904. A non/SCV 1904 would be an advantage for the end carbs on a tri-carb setup.
Adios, David

Howe-D back

I'm convinced it's true that Carburetor is French for "Don't F%#& with it..."


If we are speakin' the same jargon, I believe the 1904 with the SCV valve is the exception . the 1904 was used on many different vehicles from IHC' to Fords through the early sixties. I am under the belief the SCv was used on the Falcon but not most others.

The mothballed Clifford built 250 I had the good fortune to turn up, was equipped with three extremely clean rebuilt and modified 1904's with SCV's. They look great and have some interesting mods' like milled airhorn to allow standard air cleaners, removed, and filled choke shafts as well as plugged vac ports (Duraspark dizzy). I prudently fired up the engine initially with a "known" good running YF in the center position and progressed to single 5200 and then a 350 CFM 7448 while working on various other "issues" .

I got back to the Offy 3X1 setup and tested each of the Clifford modded carbs individually on my stock Falcon 170 "test bed" . I was very disappointed to find only one of the Holleys ran decently. The Clifford setup used a "big" 1904 with the 1-9/16" base in center and 1-7/16" base front and rear (rear one ran good). After rebuild kits and many hours of testing I got nowhere and was frustrated. http://fordsix.com/forum/viewtopic.php? ... highlight=).

So I got mad and determined. I started cruising E-Bay for 1904's and found they show up regularly and there are many versions. I started picking up a few - often they go cheap but clean ones, especially glass bowl types get a good price. The great majority DO NOT have the SCV. They are categorized (App' & CFM) by the "List Number" but I've not found two the same.

I test each one on the 170. A couple ran good untouched and I'm experimenting swapping metering blocks, jets etc. with some success. I've got a few that I just can't figure out and a few running great.

Here's a "typical-generic" - "small" 1904 supposedly for '53 Ford. It differs from the newer Falcon 1904's in that the Choke linkage is reversed, the accel pump cam is metal and no SCV's. :
-

-

Here's a "big" 1-9/16" base 1904 with large venturi. This one has a weird choke plate with integral diffuser and the fuel feed tube IS the choke shaft. (Only one I've seen):

Differences between them are mainly the base and venturi size. Some have marked main jets - most don't.

I would appreciate any comments and corrections to my understanding.

The 250 - Offy setup is running awesome currently with the one good Clifford modded carb rear, a mixed parts "big" carb center and a good $20 - 1908 front. I have gotten two "small" carbs with glass bowls running good to put front/rear but have no luck with the other two Clifford mod carbs (for now).

There are lots of low price carbs available. I paid less than $20 for most , currently waiting for this one to add to the bunch:

http://cgi.ebay.com/ebaymotors/ws/eBayI ... 0053754497

Lots more at:
http://smg.photobucket.com/albums/v296/ ... 20EXHAUST/

Powerband 8)

 

[CZLN6]

Howdy All:

Thanks PB. That was a nice survey. As soon as I started reading I realized my comments about 1904 and SCVs was too narrow. I was only thinking of Falcon Six application. The small one barrel, side bowl Holleys were used in on AMC early sixes as well.

I guess I've got to take the blinders off. Thanks again.

Adios, David

 

[jahearne]

Here's a "big" 1-9/16" base 1904 with large venturi.

Those carbs, I think, are Holley 1960. I recently purchased a manual for 1904 and it lists a 1960 with it.