429 SCJ Carburetor question

[cjstaci]

I have the original Holley 780 from the Torino Cobra that I had back in the late 70’s. I am in the process of rebuilding it. The factory SCJ had a healthy solid lifter cam so they used primary throttle plates with an 1/8” hole.
My question is; if I put this on an engine with a stock smooth idle cam, will the 1/8” hole allow too much air for it to idle correctly?

 

[TommyK]

Not doubting you but that's the first I have heard that the Holley equipped 429 SCJ's had holes in the butterflies. There is no mention of that on the megasite and the one picture they have where the butterflies are visible there are no holes that I can see.

To answer your question, you will probably have difficulty getting the engine to idle correctly with a carb that introduces too much air under the throttle blades on an engine that doesn't need it. it's basically a vacuum leak at that point.

 

[Spike Morelli]

I tend to concur, this is the first I've heard of holes in the primary butterflies as well. Years ago, some people did drill those holes to help idle quality in modified engines but I assume Ford wouldn't have tuned their engines from the factory as such. Today, Holley produces racing carbs with that air bleed feature as a tunable screw down the threaded hole where the air cleaner stud resides, so that practice of drilling "on purpose" air leaks, is not really a thing anymore.

 

[cjstaci]

I bought the car with 77k miles on it in 1977, so it’s very possible the previous owner drilled holes. I assumed it was all original, but I was 17 years old and didn’t know very much back then. I replaced the carb in 1980, so it’s been in a box ever since then.

Currently, I have it apart. The throttle shafts feel like they have too much play. It feels like 0.010” but I will check it with a dial indicator. The coating is worn off of the shafts bearing surfaces. From what I understand the coating they used was a ptfe, I am guessing it wasn’t very thick, maybe 1 or 2 mil thick. It seems like I will need to bush it, which sucks because I really would like to keep it as original as possible.

 

[cjstaci]

You sparked my curiosity. I checked the throttle plates and compared them to the new ones I have, the holes are exactly in the same location. This leads me to believe that they weren’t drilled. I looked at the picture s on the megasite and looking down from the top of the carb with the carb sitting on cardboard, you can’t see if there’s a hole in plates, it’s too dark. I checked Mustang tek and found good pictures and could see they have holes in the primary plates.

I just checked the play for the throttle shaft and it’s 0.007”. I can’t find anything from Holley but online searches seem to have varying opinions on what is acceptable wear. I saw people’s opinions vary from 0.002 all the way to 0.010. I am thinking I will reassemble as it is and see what happens. I live at 5000’ elevation so the vacuum readings are lower than sea level. The engine I want to put this carb on is a 400 and it idles at slightly over 13 in vacuum. I can’t remember what my SCJ vacuum was at idle, I think was about 12 in but at this point that’s just a guess.

 

[TommyK]

Very interesting

 

[Spike Morelli]

Yes, very interesting. Maybe ....?

 

[Hemikiller]

I would contact Drew at AirFuelSpark. all he does is Ford Holley carbs.

https://www.afscarbs.com/

He has a FB page for the business as well.

https://www.facebook.com/AirFuelSParkTech

 

[Precision Transmission]

I second contacting Drew. He has all the specs, and can set you up with the right kit,too.

 

[t.kohlmeyer]

You sparked my curiosity. I checked the throttle plates and compared them to the new ones I have, the holes are exactly in the same location. This leads me to believe that they weren’t drilled. I looked at the picture s on the megasite and looking down from the top of the carb with the carb sitting on cardboard, you can’t see if there’s a hole in plates, it’s too dark. I checked Mustang tek and found good pictures and could see they have holes in the primary plates.

I just checked the play for the throttle shaft and it’s 0.007”. I can’t find anything from Holley but online searches seem to have varying opinions on what is acceptable wear. I saw people’s opinions vary from 0.002 all the way to 0.010. I am thinking I will reassemble as it is and see what happens. I live at 5000’ elevation so the vacuum readings are lower than sea level. The engine I want to put this carb on is a 400 and it idles at slightly over 13 in vacuum. I can’t remember what my SCJ vacuum was at idle, I think was about 12 in but at this point that’s just a guess.


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I have that exact carb at home in my garage! I bought a 429 SCJ out of a Torino Cobra about 42-43 years ago for a pittance. Complete from carb to oil pan! The guy asked me if I was interested in a 429 from a Torino. He described it to me and I realized what he had. I asked him how much. He said he'd like to get $125 for it. I tried not to react too strongly, so I looked at him for a minute and said I'll give you $115 cash. He said "you've got a deal". I handed him $20 in earnest money, drove home and got my pickup truck and headed to his place. When I got there it was indeed an SCJ! When I went through it more closely I found that one rod was a standard rod. There's a guy who used to race a '71 SCJ Mach 1 near me so I stopped by his place just to see if he had an extra rod. He came back from his parts room with one in his hand. It even had the cylinder number stamped in it from the one I had that was incorrect! Easily the best deal I've ever made.

I'll check mine when I get home for the holes in the primary throttle plates.

 

[cjstaci]

I have that exact carb at home in my garage! I bought a 429 SCJ out of a Torino Cobra about 42-43 years ago for a pittance. Complete from carb to oil pan! The guy asked me if I was interested in a 429 from a Torino. He described it to me and I realized what he had. I asked him how much. He said he'd like to get $125 for it. I tried not to react too strongly, so I looked at him for a minute and said I'll give you $115 cash. He said "you've got a deal". I handed him $20 in earnest money, drove home and got my pickup truck and headed to his place. When I got there it was indeed an SCJ! When I went through it more closely I found that one rod was a standard rod. There's a guy who used to race a '71 SCJ Mach 1 near me so I stopped by his place just to see if he had an extra rod. He came back from his parts room with one in his hand. It even had the cylinder number stamped in it from the one I had that was incorrect! Easily the best deal I've ever made.

I'll check mine when I get home for the holes in the primary throttle plates.

Very cool story. You should have been arrested for stealing, lol. I am sure it must have been hard to keep cool about it. Back in the 70’s, most people didn’t realize the rarity of these cars and the specific running gear. When I bought the Torino, I was 17, all I knew about it was it was a 429 with a 4 spd. When I first saw the car I was sold. It was calypso coral with the hood black out and the shaker scoop. I paid $1175.00 for it. That was a lot of money for me back then.
When I was 18, I bought a BOSS 429 with 13,800 miles on it for $6800. The engine had been built with nascar race parts by Holmon&Moody. When I sold it in 1985 for $20,000 I thought I made bank on it. Apparently my crystal ball was broken.
Speaking of good deals, around 2012, I saw a Craigslist ad selling a toploader 4 spd. For $700. I went to the guys house, turned out it was a big input and output and the gear reduction unit attached. At that point I knew what it was and like you, knew I had to play it cool. He had lots of ford stuff, turns out he had the rear end from the same car, a 3.91:1 31 spline n case, complete drum to drum with parking brake cables attached. Now my heart was beating faster. I ended up buying it all including a brand new in the box Hurst vertigate shifter for $1100. I had suspected this guy was on crack, when I gave him the money, his wife snatched it and took off, I assumed it was to score crack. I wish I had more money because he was selling a 428 CJ and a 427.

Anyway I sent an email to Drew, hopefully he will respond and clarify a few things for me about the carb. I am curious to know about yours too.

 

[t.kohlmeyer]

I'll go look at the carb later and snap some pics. I scored a 428 CJ back in 1986. All disassembled, he had been buying bits and pieces for years and never got around to assembling it. I kinda went off the deep end on that one. My machine shop guy was an old Hemi Dart racer and he gave me a ton of advice. Polished and volume matched the chambers, Manley pro flow valves, I even notched to tops of the cylinders to match the chambers. Hooker SC headers, Edelbrock F427 intake. Polished and shot peened rods, roller rockers, 800 Holley DP, and it's in my '67 S code Hunter green fastback Bullitt clone. I think I paid $400 for the entire engine. I got the car, less engine, for $800. The guy pulled to engine and put it in his pickup truck, then set the car in his driveway for sale!

I'd have had to have that 427, no question, especially a side oiler.

 

[cjstaci]

I'll go look at the carb later and snap some pics. I scored a 428 CJ back in 1986. All disassembled, he had been buying bits and pieces for years and never got around to assembling it. I kinda went off the deep end on that one. My machine shop guy was an old Hemi Dart racer and he gave me a ton of advice. Polished and volume matched the chambers, Manley pro flow valves, I even notched to tops of the cylinders to match the chambers. Hooker SC headers, Edelbrock F427 intake. Polished and shot peened rods, roller rockers, 800 Holley DP, and it's in my '67 S code Hunter green fastback Bullitt clone. I think I paid $400 for the entire engine. I got the car, less engine, for $800. The guy pulled to engine and put it in his pickup truck, then set the car in his driveway for sale!

I'd have had to have that 427, no question, especially a side oiler.

I would love to have that car with the 428, one bad *** car. Speaking of S code Mustangs, I saw a documentary on Steve McQueens life (made in 2014). Really cool, had a couple clips of the chase scene.

 

[cjstaci]

Drew from AFS Carbs replied. He said the primary plates did come with the hole in them. He said they stamped 224, and that’s exactly what I have. He said it won’t run right if a plate without a hole is installed. He also said these plates are rare and they are part of the revised idle circuit. He also said the throttle shaft play is acceptable. He also stated I can apply a dry film lubricant that cures to the throttle shaft. He also said it should idle fine on my 400.
I have to say thanks for referring me to him. Good info.

 

[t.kohlmeyer]

I would love to have that car with the 428, one bad *** car. Speaking of S code Mustangs, I saw a documentary on Steve McQueens life (made in 2014). Really cool, had a couple clips of the chase scene.

Love that Bullitt fastback!

 

[c9zx]

Drew is the best at what he does that I know of. Chuck

 

[c9zx]

Drew from AFS Carbs replied. He said the primary plates did come with the hole in them. He said they stamped 224, and that’s exactly what I have. He said it won’t run right if a plate without a hole is installed. He also said these plates are rare and they are part of the revised idle circuit. He also said the throttle shaft play is acceptable. He also stated I can apply a dry film lubricant that cures to the throttle shaft. He also said it should idle fine on my 400.
I have to say thanks for referring me to him. Good info.

I have never worked on an 429 SCJ Holley. However it sounds like Holley or Ford got in a hurry to me. A change in the idle channel restrictor and/or idle air bleed would have cured the rich idle problem. Just my two cents. Chuck

 

[cjstaci]

I can’t speak to what Ford and Holley did in the development of the idle circuit, but I do know that if you open the throttle enough to get a satisfactory idle speed and it exposes too much of the transfer slot, then you will experience an off idle stumble. Also when too much of the transfer slot is exposed, the idle mixture screws become less sensitive. So drilling a hole in the throttle plate to have a controlled airflow allowed the idle speed to come up while keeping the throttle plate closed enough so as not to expose the transfer slot.

 

[t.kohlmeyer]

I can’t speak to what Ford and Holley did in the development of the idle circuit, but I do know that if you open the throttle enough to get a satisfactory idle speed and it exposes too much of the transfer slot, then you will experience an off idle stumble. Also when too much of the transfer slot is exposed, the idle mixture screws become less sensitive. So drilling a hole in the throttle plate to have a controlled airflow allowed the idle speed to come up while keeping the throttle plate closed enough so as not to expose the transfer slot.

You're on the mark there! If you have old late 60's early 70's Hot Rod magazines they would talk about putting holes in the primary throttle plates to keep them away from the transfer slots. I've seen it on old Holley carbs at swap meets. I used to attend the meets in the infield of the Indy 500 track (before they added the road course) and saw many of them with the holes in the primary throttle plates. Holley has since found ways to eliminate the need for this mod.

 

[cjstaci]

Here’s what a carb looks like when AFS restores one. If I had one that looked like this, I would put it in a glass case for display