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426 hemi idle #2712179
11/02/19 06:30 PM
11/02/19 06:30 PM
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antonellomopar Offline OP
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Hello
have some problems in setting the idle on my Hemicuda. The engine is running a Comp Cams 292 cam with 10.5 JE pistons and TTI exhaust. The carbs are Edelbrock 600 modified by Newcomb's Hemispherical products. I was wondering what is the correct way of setting the carbs. I have both idle blades set up to be completely closed, and the idle speed is regulated by the solenoid. The idle mixture screws on the rear carb are 3 turns out, while idle screws on the front carb are completely closed.
Car runs well, good idel but a little rich. If I turn the rear carb screws to be just two turbs out, car runs leaner, but stumbles off idle in third or fourth gear. Idle speed is set at about 800 rpm, but if I drive the car aggressively, idle speed drops to around 500, and tries to die. Any suggestions?
I also have the original carbs that were removed year ago after years of sitting. Would be a wise things to have the carbs restored and put back in place? Are they enuogh for the 292 cam?
Here in Italy nobody knows anything about Hemis so I dont really have nobody that can get the car to idle correctly. Thank you for the help

Re: 426 hemi idle [Re: antonellomopar] #2712183
11/02/19 06:47 PM
11/02/19 06:47 PM
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Might try contacting Newcomb's as they set up the carbs beer

Re: 426 hemi idle [Re: TJP] #2712185
11/02/19 06:55 PM
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antonellomopar Offline OP
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Think Newcomb is not active anymore

Re: 426 hemi idle [Re: antonellomopar] #2712190
11/02/19 07:08 PM
11/02/19 07:08 PM
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Ignition is likely playing a part. Set initial timing at 20, add 18 for 38 total and see what happens.

Re: 426 hemi idle [Re: ScottSmith_Harms] #2712256
11/02/19 10:08 PM
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What do you mean by idling off the solenoid? How are these carbs modified? Normally you have to get some air flow via the rear carb idle speed screw to set idle. Are you using progressive linkage?

Re: 426 hemi idle [Re: dragon slayer] #2712299
11/03/19 02:31 AM
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It means that the screw that controls idle is combletely backed out...leaving idle speed to the solenod. Will try to play with the front carb idle mixture screws...and see ehat happens

Re: 426 hemi idle [Re: antonellomopar] #2712323
11/03/19 09:05 AM
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Ok, I am not as familiar with 70-71 hemi carbs as the early versions. But if you look at the service procedure in the 70 manual, you set idle with the idle speed screw to 750rpm. Use the mixture screws to get highest idle rpm, then go into idle speed solenoid adjustment with the solenoid and set rpm to 900 at, 1000 st. Then back of idle screw for a lower curb idle with solenoid off. Now how those edelbrocks are set up versus original I don't know.

Seems odd to me that the mixture screws on front carb are full closed. Normally you balance them, and front carb should contribute some to the idle.

Re: 426 hemi idle [Re: dragon slayer] #2712390
11/03/19 12:42 PM
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Originally Posted by dragon slayer
Normally you balance them, and front carb should contribute some to the idle.
iagree
Open the front idle mixture screws to 1 1/5 to 2 full turns out from gently bottom all the way in and do the same on the rear screws and see how that does scope wrench
Once you do that you should be able to adjust them so the idle mixture is not rich by turning them in, all four, a 1/4 turn at a time, to make it the best idle mixture.
I've never seen a idle solenoid on a stock street hemi motor but all the ones I've raced and work on where from 1966 to1969 except my 1970 Baracuda stick shift car back in the mid 1970s, it had a 1968 stick shift motor in it when I got it. I did buy and use a set of 1970 carbs later to race it in NHRA stock class for two yearsconfused
You shouldn't need that solenoid to make your car run good and idle good twocents
Does the rear carb have the choke working? If not do you think you need it to work for cold start up? What city or part of Italy are you in ? What altitude?
If you do have the original carbs for that motor they should work a bunch better than smaller ones do at WOT twocents work
Mopar spent a bunch of time with Carter Carb. company getting the stock carbs jetted and set up to run well on the street hemi cars up
Scott Harms may be able to restore those carbs for you, he is a member on here also scope
Let us know what you do and the results thumbs


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Re: 426 hemi idle [Re: Cab_Burge] #2712396
11/03/19 12:56 PM
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don't shut off the idle fuel supply to the front carb. you idle off all 4 primary bores and you don't have factory smog carbs. if your using an electric choke on the back carb, similar to factory; then the mixture screw next to the choke will want to be about one turn further out than the other three due to extra air flow being pulled thru the choke. idle jets should be around .033"-.036" for good idle quality. step up springs may need a changed from the oranges to something lighter with that cam. somewhere around 1 1/2 turns out on the three non-choke bores and about 2 1/2 turns out for the choke with proper idle jet size should work well.

Re: 426 hemi idle [Re: lewtot184] #2712486
11/03/19 05:02 PM
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Thanks to everybody who has given me some advice. Will try in the next few days to adjust the idle as per your suggestions, and will try the car as soon as rain stops. Thank you very much.
I live in Milano, northern Italy, at the sea level.
How much is the rating in cfm for the stock Carter carbs?

Re: 426 hemi idle [Re: antonellomopar] #2712503
11/03/19 06:25 PM
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Originally Posted by antonellomopar
Thanks to everybody who has given me some advice. Will try in the next few days to adjust the idle as per your suggestions, and will try the car as soon as rain stops. Thank you very much.
I live in Milano, northern Italy, at the sea level.
How much is the rating in cfm for the stock Carter carbs?
stock AFB's never had an air flow rating; but my guess would be around 550cfm@1.5"hg. the 600 edelbrocks have the same venturii and throttle bore sizes as stock street hemi so air flow should be similar between the two. I run two 600 edelebrocks on a ch28 intake mounted on a 440 and I simply can't say enough good things about those carbs running in pairs.

Re: 426 hemi idle [Re: antonellomopar] #2712504
11/03/19 06:30 PM
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The original street hemi carbs where rated at 650 CFM according to one of the drag racing engineers at one of Mopars old drag race seminars held in the mid 1970s up

Last edited by Cab_Burge; 11/03/19 06:31 PM.

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Re: 426 hemi idle [Re: Cab_Burge] #2712559
11/03/19 10:43 PM
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The carter data form for the 70-71 hemi carbs rated them at 570cfm.

Re: 426 hemi idle [Re: dragon slayer] #2712592
11/04/19 08:24 AM
11/04/19 08:24 AM
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Kowal Offline
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As noted above, you need both carbs to idle well.

Time to research and get a carb synchronizer tool. I use one from Dvorak Machine. You can make one, buy the basic synchro tool from Edelbrock and then use white pvc to fashion the proper adaptor for your carb mounting flange.

I messed with this for a couple of years before discovering the use of the synchro tool. Big difference. Key is getting both carbs to contribute equally at idle. When you step on the gas the rear carb takes the lead based on the linkage, but the whole thing works much better when the idle is set right. My Hemi is very responsive off idle, returns to a consistent idle every time. I have a friend with a multi carb stock 57 Chevy, the tool really helped set his car up right as well.

I have a similar cam. I run timing at about 18 degrees at idle, about 30-32 at full advance. I am running stock rods and jets on the carbs, staggered sizes as per the factory (that was important).

My car is an automatic.


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Re: 426 hemi idle [Re: Kowal] #2712651
11/04/19 12:18 PM
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After reviewing the 70 solenoid carb set up, I can see what caused your issue with using the solenoid screw to set your idle. I asked before if you are using progressive linkage like original, if you are, when you used the solenoid to adjust idle you only move the linkage for the rear carb. So the solenoid opened the rear carb primary for air flow and you were able to calibrate rear carb. But the front carb remained closed. With no air flow through front the idle mixture won't do anything. That is why you have to get both carbs in balance at idle using the idle screws on the body to calibrate them. Once you have idle mixture correct you can change the balance of front to rear idle and set your solenoid idle.

What is the carb mods done? Not familiar with their product. Not sure any of the specific setting will help you since it really depends on your car specifics beyond what is mentioned, and the carb set up. Hemi carbs are much different then Edlebrock and the Hemi clones. Staggered jetting, different throttle bore depth, different primary venturi type, distribution tabs, even choke return is different. Hemi carbs return choke air to BOTH primaries so you will not see as large a difference in mixture adjustment screws.

But your using modified edelbrock so you will have to figure out the combo that works. But it is good advice to make sure you have your ignition set up right first.

Re: 426 hemi idle [Re: dragon slayer] #2712729
11/04/19 04:12 PM
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Thank you for all the suggestions. Have opened the idel mixture screws on the front carb, and idle and drivability have improved. But still not 100% satisfied. Will try to play with the idle screws on both carbs tomorrow, and see what happens. In the meantime, I am talking with Scott about rebuilding and calibrating the original carbs. Will keep the Newcomb setup until carbs will be ready.

https://www.youtube.com/watch?v=SgsEua9shGA

Made video this morning...sound is not crisp as I want. But still work to do

Re: 426 hemi idle [Re: antonellomopar] #2712741
11/04/19 04:57 PM
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Originally Posted by antonellomopar
Thank you for all the suggestions. Have opened the idel mixture screws on the front carb, and idle and drivability have improved. But still not 100% satisfied. Will try to play with the idle screws on both carbs tomorrow, and see what happens. In the meantime, I am talking with Scott about rebuilding and calibrating the original carbs. Will keep the Newcomb setup until carbs will be ready.

https://www.youtube.com/watch?v=SgsEua9shGA

Made video this morning...sound is not crisp as I want. But still work to do
idle quality is directly related to idle jet size. measure your idle jets first.

Re: 426 hemi idle [Re: dragon slayer] #2712823
11/04/19 08:57 PM
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Originally Posted by dragon slayer
The carter data form for the 70-71 hemi carbs rated them at 570cfm.

I've never heard of that form but I don't call Carter or go to their web site to look up carbs specs either realcrazy
My comments on the CFM ratings on the OEM stock street hemi carbs CFM are all based on information provided by Chrysler employees in their Direct Connection catalogs and race pamphlets and later in their drag racing bibles shruggy
I do remember that the 1966 and 1967 where originally rated at either 600 CFM or 625 CFM, depending on who was speaking and the1968 to 1971 carbs flowed 650 CFM shruggy
I've owned a bunch the early Carter carbs all the way from early 1957 AFB and all the way up to the later OEM Street Hemi carbs as well as the after market Hi Po Competition Series carbs. 500 CFM,625 and 650 CFM as well as the 750 CFM carbs shruggy
I've heard that Carter, Rochester and Holley didn't used the same methods on determining CFM ratings on their carbs work
The stock OEM Carter Street Hemi carbs look a lot like the Carter 650 CFM Competition did inside other than having the larger top for the larger diameter air cleaner lids shruggy


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Re: 426 hemi idle [Re: Cab_Burge] #2712838
11/04/19 09:32 PM
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Go to www.diamondbackengines.com and click on the "white papers" at the top of the home page. There is a well written procedure for setting up dual quad carbs,

Re: 426 hemi idle [Re: Cab_Burge] #2712874
11/04/19 11:44 PM
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Originally Posted by Cab_Burge
Originally Posted by dragon slayer
The carter data form for the 70-71 hemi carbs rated them at 570cfm.

I've never heard of that form but I don't call Carter or go to their web site to look up carbs specs either realcrazy
My comments on the CFM ratings on the OEM stock street hemi carbs CFM are all based on information provided by Chrysler employees in their Direct Connection catalogs and race pamphlets and later in their drag racing bibles shruggy
I do remember that the 1966 and 1967 where originally rated at either 600 CFM or 625 CFM, depending on who was speaking and the1968 to 1971 carbs flowed 650 CFM shruggy
I've owned a bunch the early Carter carbs all the way from early 1957 AFB and all the way up to the later OEM Street Hemi carbs as well as the after market Hi Po Competition Series carbs. 500 CFM,625 and 650 CFM as well as the 750 CFM carbs shruggy
I've heard that Carter, Rochester and Holley didn't used the same methods on determining CFM ratings on their carbs work
The stock OEM Carter Street Hemi carbs look a lot like the Carter 650 CFM Competition did inside other than having the larger top for the larger diameter air cleaner lids shruggy


You never heard of the carter service manual? It has all the technical specs on the airbleeds, jets, venturi dia, etc, plus all the part number for the various parts. Just like the Holley book. So it is just another number you can add to your one Chrysler guy said 625 and another 650, and another??? Isn't that even crazier to have one source tell you several different answers/hearsay??

I have broken down quite a few carters from the very first 57 type to the later 70s Marine AFB and modern stuff too. I examine all the venturi differences and compare them to what other manufactures did. I don't think Chrysler ever really got the hemi carbs figured completely out. Every year was a different stagger, with a jet modification. Followed by venturi mods trying to figure out distribution.

While a simple glance the original hemi and the Competition may look alike, but they are not. The Hemi carbs are more like some of the early AFB with a primary side main venturi sunk lower in the carb body, requiring a primary side primary venturi that is longer to place it at the optimal low pressure point. Many of the other AFB for Chrysler and others had a raised venturi that used a shorter primary (booster) venturi. Also the top for a hemi does not have the contoured wedge to shape flow for the secondary venturi. I don't know why, so I would really love to talk to a Carter or Chrysler engineer from those day to know what effect that had. But I doubt many if any with the knowledge are even alive anymore.

It is really interesting looking at the 60-65 AFB for GM. Buick, Cad, Pon, Chevy had significantly different approaches to how they wanted the carb set up for lets use a 389-421 CI motor across the car lines. They had carter working overtime with hardly anything common. They chose different bore sizes, different main venturi and primary sizes, had different approaches to bleed and jet size and even locations, for effectively the same big block gm motor. All this changed the Venturi Area to Throttle bore ratio. And it seemed each manufacture had their specific ratio they were shooting for. Much of this size issue is in another technical form from the carter book. Frankly one of the largest afb non race type was for the early 60s 327 corvette engine. The Bore and venturi area dwarfed the hemi carb. I think that was a 350-365hp small block.

Now a days we clone the Edelbrock, or just use them out of the box and they do work. I would love to have the resources to test them against originals on a full dyno with all the appropriate measuring devices to really see how they compare. But that won't happen.







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