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440 Six Barrel - Flat Spot #2659381
05/26/19 04:32 PM
05/26/19 04:32 PM
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A39Coronet Offline OP
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Been fighting a flat spot with this car for the last few years and hoping moparts can help again. At a slow roll (like getting onto a highway onramp) when you hammer down, the car comes alive, falls flat, and then recovers. I've tried yellow/purple/plain springs in the secondaries thinking it was an issue with the opening sequence, but nothing seems to change it. I swapped manifolds from iron and aluminum strickly to reset the carbs on the bench. New diaphragms, reset everything back to OE, new coil and distributor, even installed a brand new center carb due to a PITA fuel leak. Timing set at 18/32/52 with vac advanced hooked up. Other than this issue, car drives without a problem.

This was my dad's car, and knowing him, the engine and cam would be all OE or thereabouts. That's all the info I can provide unfortunately.

The only item I'm not fond of is he had promax go through the secondaries back in the early 2000s, and it has their billet metering plates with 84 jets. I have no clue if these are right, or if this is part or all of the issue. Haven't got around to calling them.

Last edited by A39Coronet; 05/26/19 04:33 PM.

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Re: 440 Six Barrel - Flat Spot [Re: A39Coronet] #2659388
05/26/19 04:52 PM
05/26/19 04:52 PM
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The bog is caused by the secondary carbs. opening to quickly, try the stiffest spring you have on both pods next and let us know if that helps or not scope wrench
Do you know the List number on all three crabs? If not look at the rear passenger side of the carbs behind the venture boosters and write them down and post them on here, I can then look them up in my old Holley master catalog for the original application and specs. on them.
Mopar used a bunch of different List # Holley two barrels on the production cars, a bunch of them shock None of them are exactly alike or like the same tuning on them work


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: 440 Six Barrel - Flat Spot [Re: Cab_Burge] #2659393
05/26/19 04:58 PM
05/26/19 04:58 PM
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A39Coronet Offline OP
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Rear - "LIST-4383"
Front- "LIST-4382"

I have plain springs in there now, but was reluctant to go any stiffer because I've never seen anyone use or suggest browns (medium heavy) or blacks (heavy). I know "the car wants what the car wants", but anytime I've had to stray too far away from the norm on any of my cars, it's normally something completely different causing the issue.


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Re: 440 Six Barrel - Flat Spot [Re: A39Coronet] #2659406
05/26/19 06:24 PM
05/26/19 06:24 PM
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I would try a bigger acc nozzel on the center carb becas it sounds like it is leaning out ! Al bb setups i have workt on responded good on that and i ended up whit a 50cc pump also.

Re: 440 Six Barrel - Flat Spot [Re: A39Coronet] #2659424
05/26/19 07:34 PM
05/26/19 07:34 PM
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north central IL
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Sounds familiar. My car would start out strong for about 2 seconds then fall on its face and then recover again. I thought it was the secondaries.

I eventually installed an air/fuel gauge with an oxygen sensor in the collector area of the headers. Found out that the bog was related to the accelerator pump: it would clock over way lean for 1/2 second and then recover. I changed out the 30 cc pump to a 50cc, changed out the .031 nozzle for a .021 with hollow discharge screw, and installed the brown cam #1 position. I figured out that it needed a larger pump capacity spread out over a longer interval of time. (going from .031 to 021) The 30 cc with .031 nozzle would "empty" out before the engine was through with it.
By the way I also have the Promax plates with #81 jets, and use the purple springs. Now it feels like I've been rear ended by a 100mph freight train. The AFR while accelerating sits at about 12.5 to 13.0.

This is a 440 with .030 over, Hughes HEH2832 cam,ported 906 heads with larger valves and 1.6 rockers. TTI exhaust with 3" pipes. 727 trans with 3.55:1 gear

Once you get this figured out it will be your favorite induction system. It sure is mine.

Re: 440 Six Barrel - Flat Spot [Re: A39Coronet] #2659428
05/26/19 07:43 PM
05/26/19 07:43 PM
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A39Coronet Offline OP
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Pump shot was my next move based on today's test with the plain springs producing no change to the flat spot. Gonna yank carbs off tomorrow and do some swapping. Ive been wanting to get a gauge rigged up but just aren't equipped to get it done at the moment.

I'm keep telling myself "this is the fun part"


Follow my G3 Hemi Barracuda build on Youtube
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Re: 440 Six Barrel - Flat Spot [Re: A39Coronet] #2659429
05/26/19 07:46 PM
05/26/19 07:46 PM
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Originally Posted by A39Coronet
Pump shot was my next move based on today's test with the plain springs producing no change to the flat spot. Gonna yank carbs off tomorrow and do some swapping. Ive been wanting to get a gauge rigged up but just aren't equipped to get it done at the moment.

I'm keep telling myself "this is the fun part"



I'm watching this thread. Please post results


[img]http://www.imgur.com/hxlGUJt.gif[/img]
4-speed
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Re: 440 Six Barrel - Flat Spot [Re: 70sixpkrt] #2659456
05/26/19 08:50 PM
05/26/19 08:50 PM
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N.E. Ohio
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Put a toothpick in the vacuum lines.
Kill bleeds are too big


70` Cuda`,440 6BBL Jerico,Dana 4.56 Still on 93 Pump Gas
9.87 @ 136/1.31-60ft.`09 Mopar Nationals PASSON PERFORMANCE "Stick-Shift" Champ!
2013 StickShift Challenge Winner@ Mopar Nationals!
Re: 440 Six Barrel - Flat Spot [Re: 6bblFLASH] #2659474
05/26/19 09:44 PM
05/26/19 09:44 PM
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A39Coronet Offline OP
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Originally Posted by 6bblFLASH
Put a toothpick in the vacuum lines.
Kill bleeds are too big


I'm not sure what kill bleeds are...could you give further details?


Follow my G3 Hemi Barracuda build on Youtube
https://www.youtube.com/watch?v=XSDAWczXoZw&list=PLTus_wQu8POADHEeJNJp2nr4NMHEyB9EK

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Re: 440 Six Barrel - Flat Spot [Re: A39Coronet] #2659478
05/26/19 09:54 PM
05/26/19 09:54 PM
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Bend,OR USA
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Originally Posted by A39Coronet
Pump shot was my next move based on today's test with the plain springs producing no change to the flat spot. Gonna yank carbs off tomorrow and do some swapping. Ive been wanting to get a gauge rigged up but just aren't equipped to get it done at the moment.

I'm keep telling myself "this is the fun part"

I had a mix of 1970 440 automatic carbs. on my old pump gas Duster low deck stroker motor(511 C.I.) that had the stock 30 CC pump and #33 squirters in it, I ended up using a small bolt and nut on it in the return slot on the center carb. to force the outboard carbs to open sooner, no bog once I got the carbs right. Have you mess with the idle mixture screws on the outboard carbs yet? If not to that, even if you have to remove the lead plugs wrench Try setting them at 1/3 to 3/4 turn out from being bottomed out completely closed scope thumbs
BTW, if you don't try what others haven't or won't, how will you find out what YOUR car really wants and needs work grin wrench

Last edited by Cab_Burge; 05/26/19 09:56 PM.

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Re: 440 Six Barrel - Flat Spot [Re: A39Coronet] #2659500
05/26/19 11:03 PM
05/26/19 11:03 PM
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Taxes & Virus's R-US, NY
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You are not going to like my answer, but your like one of those stubborn friends I have that loves those things......Lets start with the basics.....Its a six pack carb setup. That means its got one carb, and two vacuum out boards. It only has one squirter, and the rest relies on the vacuum from the engine. This is not a good way to make things work.

You want to fix it, put three center "carbs" on it....or throw it out and go with dual fours or a big single. You won't change the strips on the Zebra...You have to switch it out.

Got a friend, he loves those carbs. Knows everything there is to know about them. He has been putting them on every bbm he has ever owned, guess what he is running right now? Two Eddy Thunder series carbs...no flat spots, and runs 9.84 to the six packs 10.30's.....same everything else.

I can give you his name and number if you want. I couldn't even begin to tell you all the mods he has done to them and dyno time spent. All to be out run by a simple 950 four barrel....I have the vids to prove it too....

Call me an idiot, I don't care, but those things might look really neat, but in essence they are a big vacuum modulator....The engine, to over come the vacuum needs fuel, and a squirter is how you avoid the lean spot....No squirter, you get a big lean spot. Chrysler's like fuel, and you have to give the engine what it wants.

This weekend he tested two new AVS2 carbs vs. the Thunder series...I got the vid on that too...Don't get me wrong, I like Mopars and Six packs, but unless you launching at a high enough rpm to no longer need the squirter, you have a flat spot.

Last edited by Dragula; 05/26/19 11:08 PM.

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https://www.youtube.com/watch?v=JCvfzsC4NgM (9.9)

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Re: 440 Six Barrel - Flat Spot [Re: Dragula] #2659511
05/27/19 12:25 AM
05/27/19 12:25 AM
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huh must be sumpin wrong wit ma six pack i cant find the flat spot !

Re: 440 Six Barrel - Flat Spot [Re: calrobb2000] #2659523
05/27/19 06:26 AM
05/27/19 06:26 AM
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All the springs in the outboards do is control the rate they open not when. You may need to adjust the kill bleeds. It is very easy to do.

carbs5.jpg

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Re: 440 Six Barrel - Flat Spot [Re: calrobb2000] #2659524
05/27/19 06:28 AM
05/27/19 06:28 AM
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Originally Posted by calrobb2000

huh must be sumpin wrong wit ma six pack i cant find the flat spot !


i have a set of the flat spotless ones too. I did have to spend a little time on the kill bleed/spring combo. I had a link showing the kill bleed location, but I can't seem to find it now.

Whatever you try, don't flood it with excessive center squirter size. mine is .035 and it's on a mild 440 in a D150


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Re: 440 Six Barrel - Flat Spot [Re: A39Coronet] #2659525
05/27/19 06:37 AM
05/27/19 06:37 AM
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Originally Posted by A39Coronet
Originally Posted by 6bblFLASH
Put a toothpick in the vacuum lines.
Kill bleeds are too big


I'm not sure what kill bleeds are...could you give further details?




The "kill-bleeds" are in the outboard venturi ,and like the one in the primary venturi use airflow to generate a vacuum. Basically a ported vacuum source,only it take significant airflow/load to generate a signal.
The springs control RATE of opening . Think of a shock absorber on the suspension.
Kill-bleed controls WHEN.

Really need to know a lot more about your car to help more than that

Everyone is 100% accurate,,,secondaries are opening too soon.
Is it smooth from off idle to the floor?
A long shot,but I have seen the linkage drag the secondaries open enough to give odd results.

I can tell you this: smooth transition under ANY condition is doable............BUT tuned for best E.T.`s will NOT be ideal under ALL conditions.
Traction,RPM when called upon and manifold vacuum when "nailing" it will all want something a little different.
Not to say a "race" tuned 6bbl is not a good streetcar,it just can`t do EVERYTHING 100% if tuned for one purpose.
4bbls can`t do this either,,,enter EFI and computers.............


70` Cuda`,440 6BBL Jerico,Dana 4.56 Still on 93 Pump Gas
9.87 @ 136/1.31-60ft.`09 Mopar Nationals PASSON PERFORMANCE "Stick-Shift" Champ!
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Re: 440 Six Barrel - Flat Spot [Re: 1DGEMAN] #2659528
05/27/19 06:42 AM
05/27/19 06:42 AM
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Originally Posted by 1DGEMAN
All the springs in the outboards do is control the rate they open not when. You may need to adjust the kill bleeds. It is very easy to do.




I was going to post this also up

Good article,explains it all very well. Chrysler Power mag. 1992?


70` Cuda`,440 6BBL Jerico,Dana 4.56 Still on 93 Pump Gas
9.87 @ 136/1.31-60ft.`09 Mopar Nationals PASSON PERFORMANCE "Stick-Shift" Champ!
2013 StickShift Challenge Winner@ Mopar Nationals!
Re: 440 Six Barrel - Flat Spot [Re: A39Coronet] #2659529
05/27/19 06:44 AM
05/27/19 06:44 AM
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The most common mistake - and you have made it - and the rest of you just ignore...no one wants to baseline the carbs.
whistling
The engines response to the secondaries is totally determined by how well the carbs are set up as one. Your set up is not correct so you may continue to chase your tail until you choose follow proper technical information. Stop listening to the nannies who have poor knowledge about making a six pak work.
drive
You are not drag racing based on your post so this may not be the right place as there is only WOT here.
fury
There is plenty of proper documentation to assist one in setting up a six pak properly. purple
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Re: 440 Six Barrel - Flat Spot [Re: ThermoQuad] #2659546
05/27/19 08:52 AM
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I appreciate everyone's feedback. I have the 71' service manual, gonna dig through it again to see if anything else jumps out at me. Also looks like I have a new list of items to check with kill bleeds ect.

As far as getting rid of the six-pack setup for something else, ain't gonna happen. It's an original 440+6, which used to run great when I was a kid.

Originally Posted by ThermoQuad
The most common mistake - and you have made it - and the rest of you just ignore...no one wants to baseline the carbs.
whistling
The engines response to the secondaries is totally determined by how well the carbs are set up as one. Your set up is not correct so you may continue to chase your tail until you choose follow proper technical information. Stop listening to the nannies who have poor knowledge about making a six pak work.
drive
You are not drag racing based on your post so this may not be the right place as there is only WOT here.
fury
There is plenty of proper documentation to assist one in setting up a six pak properly. purple
There is a saying in the world of technical support RT@#$%^&*M
Read the manual, so read the guide. help
wrench



Obviously it's ideal but considering I'm dissecting old equipment with little to no history, it's a challenge. Also hard to go back to the baseline with the questionable promax setup. May even try to get stock metering plates in during the next summit order.


Follow my G3 Hemi Barracuda build on Youtube
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Re: 440 Six Barrel - Flat Spot [Re: A39Coronet] #2659692
05/27/19 05:23 PM
05/27/19 05:23 PM
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Update:. Changed from OE white cam to #2 orange cam and .021 nozzle with no change. Disconnected the secondary vac lines and drove around just on the center carb and it was flawless (obviously down on power but no issue).

Next route is to revisit the 84 jets with Promax. Haven't ruled out need to mess with kill bleeds but want to try everything else first since thst involves tapping the carb body and an order to McMaster Carr.


Follow my G3 Hemi Barracuda build on Youtube
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Re: 440 Six Barrel - Flat Spot [Re: A39Coronet] #2659696
05/27/19 05:27 PM
05/27/19 05:27 PM
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If you haven't reset the idle mixture on the outboard carbs do that next, it will help up scope


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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