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Old 03-04-2012, 10:20 PM
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Dual Quads on 1956 Pontiac factory set up

HA ! Is there anyone out there who knows anything about the 1956 Pontiac cars with the OEM factory Dual Quad carb. set up they used on the Nascar in 1956? If so I sure would like hearing from you. I just put a engine together from a 1957 Pontiac 347 cu.in. and put the 1956 dual Quad on it . I'am having Trouble getting it to Idle down to a smooth idle like it had with the single four barrel carb. Any help on this will be appreciated . Thanks Roger.

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Old 03-04-2012, 10:40 PM
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My first guess would be that you have a vacuum leak. Spray Carb cleaner at the base of the carbs and near the manifold/head mating surfaces. If the engine reves up, you have found a vacuum leak.
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Old 03-06-2012, 10:04 PM
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Dual Quads on 1956 Pontiac

Hi WDCreeck, Thanks for the tip but I already tried that. Came up with no leaks! Since I made my post I have found that the engine is over fueled at a Idle. What I need to do is find a way to shut down the idle curcuit on the secondary carb. The reason I know this I installed a plate under the one carb. and it idles just like it did with the single 4 barrel on it. Then I removed the plate and put it under the other carb. and it runs perfectly just like it did before I put the dual quads on. So I came to the conclusion that I need to shut the idle curcuit down of the secondary carb. Now my problem is I don't know what holes to block off to shut the idle curcuit down. These are the original carbs. that came on the 1956 Pontiac on the 4 Barrel engines. They are the old Rochester 4 barrels that was used on many G.M. cars back in the mid 1950's. I know that there is someone out there that knows what holes to shut down, if I can only find them! Thanks , starchiefcustom
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Old 03-07-2012, 08:11 AM
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You might do well to search for info on the Chevy carbs. I think they were Carter WCFBs, and I bet they were the same. There will be a lot more info on out there for those.
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Old 03-15-2012, 10:10 PM
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Dual Quads oon a 1956 Pontiac factory set up

I think I can help you. I'm an old guy and my first sighting of that engine was on the show room of a Pontiac dealer with the ad, "New, High Performance Pontiac V-8, 265 HP." That got my attention. I spoke to the salesman (who didn't know too much about performance engines) and then I went out to their shop and spoke to a Tech who raced with us. He told me, "That thing flies!" I took it for a drive with my dad later in the week. It did run. My buddy bought it (a premium price too) and he went right to work on it to get it ready for the 1/4 mile drags. That car really did run good. I'll have to look in my photo's. I know I have some engine photo's from long ago. Probably B & W too. I know the '56 Chevy 265's were out with dual quads too and he'd beat them repeatedly. Whay questions can I help you with?
Normbc9
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Old 03-15-2012, 10:14 PM
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Dual Quads on a 1956 Pontiac factory set up

I can tell you his only had the idle on the front carburetor and has a progressive linkage that opened the rear carburetor after about a 1/2 inch of throttle. They were Rochester's and I'd ask a Poncho person to help to refer you to a shop where the idle from the second carburetor could be removed. Try "Dickshotrodplace" in Franklin. IN.
Normbc9
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Old 03-16-2012, 08:46 PM
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Quote:
Originally Posted by starchiefcustom
HA ! Is there anyone out there who knows anything about the 1956 Pontiac cars with the OEM factory Dual Quad carb. set up they used on the Nascar in 1956? If so I sure would like hearing from you. I just put a engine together from a 1957 Pontiac 347 cu.in. and put the 1956 dual Quad on it . I'am having Trouble getting it to Idle down to a smooth idle like it had with the single four barrel carb. Any help on this will be appreciated . Thanks Roger.
Have you tried simply lightly bottoming the idle mixture screws of the "secondary carb" (the one you do not want to contribute any idle mixture)? This will in effect remove the idle mixture from it, allowing the engine to idle off of the "primary" 4-barrel.

You could still be rich off-idle, depending on how the transition circuits of these carbs are set up. If they're a pair of single 4-barrel application carbs for instance, they could be rich across the board.

In any event, I'd start w/what I suggested at first and see what the results were.
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Old 03-18-2012, 09:44 PM
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Quote:
Originally Posted by TucsonJay
You might do well to search for info on the Chevy carbs. I think they were Carter WCFBs, and I bet they were the same. There will be a lot more info on out there for those.
Hi Tucon Jay, I will keep my eyes open for some of those carbs. Also I'll read up on them and see if they will work ok on my manifold. Thanks for your help on this. Roger.
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Old 03-18-2012, 10:35 PM
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Quote:
Originally Posted by Highball
I think I can help you. I'm an old guy and my first sighting of that engine was on the show room of a Pontiac dealer with the ad, "New, High Performance Pontiac V-8, 265 HP." That got my attention. I spoke to the salesman (who didn't know too much about performance engines) and then I went out to their shop and spoke to a Tech who raced with us. He told me, "That thing flies!" I took it for a drive with my dad later in the week. It did run. My buddy bought it (a premium price too) and he went right to work on it to get it ready for the 1/4 mile drags. That car really did run good. I'll have to look in my photo's. I know I have some engine photo's from long ago. Probably B & W too. I know the '56 Chevy 265's were out with dual quads too and he'd beat them repeatedly. Whay questions can I help you with?
Normbc9
Hi, The problem I'am having is the carbs. I have are for a single 4 barrel factory car. The one carb. should not have a idle circuit in it. By having two regular 4 barrel carbs it is getting to much gas at a idle. I talked to a man that said all I had to do was to block off the idle circuit on the one carb. and then it would be ok. But that didn't work. It must be pulling some gas and fuel mixture through the secondaries also. It just won't idle down to a smooth idle like it should! If I block off the one carb with a plate it will Idle smooth down to 200 RPM's. What this shows me is that the other carb. is causing the over fueling problem. Maybe there is someone or you may know how to take out the idle circuit on one of the carbs. and still have the carbs. work as they did on the factory OEM dual quad carbs. cars did back in 1956! I know there is more to it then the manifold and the dual quads. There was other thing in the package for those that made them the higher H.P. But I'am only working on the idle now. If it dosen't proform correctly on the highway conditions I will work that out later. Right now my main thing is to get it to idle down to factory specs. smooth at 450 to 650 RPM's in drive possition. Thanks for your help Roger.
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Old 03-18-2012, 10:39 PM
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Quote:
Originally Posted by TucsonJay
You might do well to search for info on the Chevy carbs. I think they were Carter WCFBs, and I bet they were the same. There will be a lot more info on out there for those.
I'll do that to see if I can come up with a solution to my problems. Thanks, Roger.
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Old 03-18-2012, 10:45 PM
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Quote:
Originally Posted by Highball
I can tell you his only had the idle on the front carburetor and has a progressive linkage that opened the rear carburetor after about a 1/2 inch of throttle. They were Rochester's and I'd ask a Poncho person to help to refer you to a shop where the idle from the second carburetor could be removed. Try "Dickshotrodplace" in Franklin. IN.
Normbc9
Thanks for the imfo. I will try "Dickshotrodplace'" to see if he can help!
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Old 03-18-2012, 11:04 PM
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Starchief, I can't see that your problem is having idle circuits in both carbs. I used to run a 389 with two Carter AFBs that both had idle circuits and had no idle problem. Check to see that the butterflies ar closing completely in both carurators.

Bill

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Old 03-18-2012, 11:19 PM
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Quote:
Originally Posted by cobalt327
Have you tried simply lightly bottoming the idle mixture screws of the "secondary carb" (the one you do not want to contribute any idle mixture)? This will in effect remove the idle mixture from it, allowing the engine to idle off of the "primary" 4-barrel.

You could still be rich off-idle, depending on how the transition circuits of these carbs are set up. If they're a pair of single 4-barrel application carbs for instance, they could be rich across the board.

In any event, I'd start w/what I suggested at first and see what the results were.
Hi, I tried to set the idle screws in all the way and all other possitions also. It still runs very rich and won't idle down to a smooth idle. What you say is what is happening! It is still pulling some mixture through the throttle plates on the primary or secondary or both on the secondary carb. If I put a plate under either carb. it will idle down to 200 RPM's at a smooth idle. This is why I know it is getting to much fuel at a idle. Both carbs. are newly rebuilt and they are perfect but not for a dual quad application. Like I said I can run it on either carb with a plate under one or the other carbs. and I can idle it down to 200 RPM's with a smooth idle.I can almost count the strokes. It is to idle down to 450 to 650 RPM's in drive possition and it does it very well on one 4 barrel with the other plated off. Thanks, Roger
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Old 03-19-2012, 12:57 AM
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Quote:
Originally Posted by WDCreech
Starchief, I can't see that your problem is having idle circuits in both carbs. I used to run a 389 with two Carter AFBs that both had idle circuits and had no idle problem. Check to see that the butterflies ar closing completely in both carurators.

Bill

WDCreeck. The only thing I can think is you were running carters and these are old rochesters and they may have different idle circuits in them and maybe the carters can be totaly shut off by turning the idle screws in till they hit the seats. Just a idea I really don't know. Another thing I'am running a stock cam for the year of 1957 in this 347 cu. in. engine which is made to run at a very low max 650 RPM in drive at idle and it will with one of the carbs. blocked off and as smooth as a kitten. In most cases these cars that are running dual quads are built for high proformance and have a high lift cam and therefore they never idle at a low RPM to have a problem like I'am having. They wouldn't idle at a low 650 RPM without shutting off. I have a factory 3 two barrel carb. set up called a J-2 on a 1957 Oldsmobile and both end carbs. on that are the secondary carbs. and they do not have a idle circuit in them. The center carb is the primary carb. and it is the only one with a adjustible idle circuit. I mainly want this set up for looks not for racing anyway. The way the cost of gas is going up I like it for cruising only and the look but I do want it to work if I want to open it up once in a while! Thanks, Roger.
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Old 03-19-2012, 04:23 AM
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Quote:
Originally Posted by starchiefcustom
Hi, I tried to set the idle screws in all the way and all other possitions also.
Try backing off the curb idle screw all the way on the secondary carb. Allow there to be just the slightest amount of opening, I mean slightest, just enough so the throttle butterflies don't stick in the throttle bores.

Unless something is amiss, the secondary carb w/idle mixture screws all the way in lightly seated and w/the throttle blades closed should not be supplying any idle air/fuel mixture.
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