440 Six Barrel - Flat Spot
#2659381
05/26/19 04:32 PM
05/26/19 04:32 PM
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Joined: Dec 2016
Posts: 1,110 Usa
A39Coronet
OP
super stock
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OP
super stock
Joined: Dec 2016
Posts: 1,110
Usa
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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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Joined: Aug 2003
Posts: 43,007 Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,007
Bend,OR USA
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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 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 None of them are exactly alike or like the same tuning on them
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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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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Joined: Jan 2003
Posts: 3,675 South San Francisco, Ca
70sixpkrt
master
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master
Joined: Jan 2003
Posts: 3,675
South San Francisco, Ca
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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"
I'm watching this thread. Please post results
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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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Joined: Jan 2003
Posts: 3,830 N.E. Ohio
6bblFLASH
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master
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Posts: 3,830
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!
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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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Joined: Dec 2016
Posts: 1,110 Usa
A39Coronet
OP
super stock
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OP
super stock
Joined: Dec 2016
Posts: 1,110
Usa
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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?
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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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Joined: Aug 2003
Posts: 43,007 Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,007
Bend,OR USA
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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"
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 Try setting them at 1/3 to 3/4 turn out from being bottomed out completely closed 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
Last edited by Cab_Burge; 05/26/19 09:56 PM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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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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Joined: May 2004
Posts: 12,379 Taxes & Virus's R-US, NY
Dragula
I Live Here
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I Live Here
Joined: May 2004
Posts: 12,379
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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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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Joined: Feb 2006
Posts: 604 TN
1DGEMAN
mopar
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mopar
Joined: Feb 2006
Posts: 604
TN
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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.
Real Men shift for themselves
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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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Joined: Nov 2011
Posts: 284 PA
Harry's Taxi 2
enthusiast
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enthusiast
Joined: Nov 2011
Posts: 284
PA
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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
'86 Maple Grove KOS Mopar low qualifier......true street legal with no power adders.
NOS-used when losing since 1940.
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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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Joined: Jan 2003
Posts: 3,830 N.E. Ohio
6bblFLASH
master
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master
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Posts: 3,830
N.E. Ohio
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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! 2013 StickShift Challenge Winner@ Mopar Nationals!
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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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Joined: Jan 2003
Posts: 3,830 N.E. Ohio
6bblFLASH
master
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master
Joined: Jan 2003
Posts: 3,830
N.E. Ohio
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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. I was going to post this also 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!
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Re: 440 Six Barrel - Flat Spot
[Re: ThermoQuad]
#2659546
05/27/19 08:52 AM
05/27/19 08:52 AM
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Joined: Dec 2016
Posts: 1,110 Usa
A39Coronet
OP
super stock
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OP
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Posts: 1,110
Usa
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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. The most common mistake - and you have made it - and the rest of you just ignore...no one wants to baseline the carbs. 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. You are not drag racing based on your post so this may not be the right place as there is only WOT here. There is plenty of proper documentation to assist one in setting up a six pak properly. There is a saying in the world of technical support RT@#$%^&*M Read the manual, so read the guide. 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.
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