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440 six pack idle help #2751905
03/14/20 04:07 PM
03/14/20 04:07 PM
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Tomkcuda Offline OP
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Here we go again some of you may say. I have read bunch of information on the web about how to tune these carbs. Here is my
Issues. I have a 70 cuda with 512 stroker from 440 source, aluminum intake, fairly lopy cam (picture of cam card attatched). The car runs great with tons of power when I drop the hammer but when I come to stop, car dies. I have tried all the tricks, vacuum test, power valve changes, new jets, 1/8 to 1/4 outboard a/f idle mix screw adjustment, checked for air leaks. Currently I installed 4.5 power valve and have the choke pull off disconnected and the outer carbs mixture screw 1/2 turned out and seems to respond the best but runs very rich during low rpm when driving. Every time I fully open the center choke flap engine will stall and die. Someone said most likely a vacuum leak but I have not been able to find it. Also when I choke off the air completely on both outer carb it will stall too.
So... I am stumped and appreciate the advise in advance.

20200314_115029.jpg
Re: 440 six pack idle help [Re: Tomkcuda] #2751994
03/14/20 08:46 PM
03/14/20 08:46 PM
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I would test the power valve to make sure it is not ruptured or the gasket is leaking scope
I had a similar motor, 400 block bored to 4.375 with a 4.25 stroke crankshaft with 9.25 to 1 comp ratio with a comp Cams solid roller with 260@.050 on the intake lobes and 266 @.050 on the exhaust lobes, ground on a 108 LSA and installed 2 degrees advance so the intake lobe center was installed at 106 ATDC.
It had a low deck Eddy six pack intake with a set of OEM Holley 1970 440 6 pack carbs. with a 2.5 power valve, it would idle at 850 RPM in gear and 1000 RPM in neutral,it was a ton of fun to drive boogie
I did have to work on the carbs to get them to do that though, 1/2 turn out from bottomed out on the outboards mixture screws and right at 1.5 turns out on the center carb. No choke plate or bar in the center carb., the accelerator pump squirter was a #35 I think, I did use a screw with a nut on it in the return slot on the center carb to start opening the outboards sooner when I went to WOT, I had to try different locations on that but I think it was around 1/3 of the way from the top at idle in that slot. I did have a custom built 10 inch converter at first and later a 8 inch T/A SS race hemi converter that worked great on the street and at the track, way better than the 10 inch street and strip converter up
It will work great once you figure out what is currently wrong upscope wrench

Last edited by Cab_Burge; 03/14/20 08:49 PM.

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: 440 six pack idle help [Re: Tomkcuda] #2751999
03/14/20 09:11 PM
03/14/20 09:11 PM
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Brisbane Australia
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Originally Posted by Tom Kim
Here we go again some of you may say. I have read bunch of information on the web about how to tune these carbs. Here is my
Issues. I have a 70 cuda with 512 stroker from 440 source, aluminum intake, fairly lopy cam (picture of cam card attatched). The car runs great with tons of power when I drop the hammer but when I come to stop, car dies. I have tried all the tricks, vacuum test, power valve changes, new jets, 1/8 to 1/4 outboard a/f idle mix screw adjustment, checked for air leaks. Currently I installed 4.5 power valve and have the choke pull off disconnected and the outer carbs mixture screw 1/2 turned out and seems to respond the best but runs very rich during low rpm when driving. Every time I fully open the center choke flap engine will stall and die. Someone said most likely a vacuum leak but I have not been able to find it. Also when I choke off the air completely on both outer carb it will stall too.
So... I am stumped and appreciate the advise in advance.


What size jets are you using in centre carb.

Re: 440 six pack idle help [Re: Tomkcuda] #2752012
03/14/20 10:32 PM
03/14/20 10:32 PM
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BSB67 Offline
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If it idles better partially choked, you have a vacuum leak. Hand over the cab at idle to verify (choke fully open).

Any additional details on exactly what it does at idle without choke might be helpful info.

Make sure you have at least 25° ignition advance at idle.

Re: 440 six pack idle help [Re: BSB67] #2752050
03/15/20 08:24 AM
03/15/20 08:24 AM
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It needs to have the timing advanced. my 2cents

Re: 440 six pack idle help [Re: Tomkcuda] #2752061
03/15/20 09:35 AM
03/15/20 09:35 AM
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Start with the mixture screws on all 3 carbs out 1 1/2 turns.Put your finger over each air bleed and adjust the screw for that air bleed in or out so that when you cover the air bleed the idle does not change. Last one I set up ended up at 1 5/8 turns on all 6 mixture screws.

Re: 440 six pack idle help [Re: 572B1] #2752077
03/15/20 10:11 AM
03/15/20 10:11 AM
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#65 jets

Last edited by Tom Kim; 03/15/20 11:39 AM.
Re: 440 six pack idle help [Re: Tomkcuda] #2752082
03/15/20 10:33 AM
03/15/20 10:33 AM
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It's hard to diagnose via the internet as we can't see or hear the operation of your set up, along with just the supplied info on hand, that being said I like to start with the basics to sometimes cover the most obvious often overlooked, you gave no mention of checking/setting fuel level in each bowl, to me this is the first operational/running step after confirming all mechanical installation procedures...


I'll mention this just for sh!ts and giggles: but I've come across 2 guys so far over the years that either daunted or unfamiliar with the set up, that have installed the center carb as delivered new from Holley, unfortunately Holley attaches and clips a hose from the PCV port to the bowl vent tube (why?), yeah the set up runs! (barely), but the PCV "vacuums" the bowl dry of fuel... it's simple problems like this that can cause some to render " complex solutions to simple problems", you/we need to know that all of the basics from installation to operational set up have been performed

Mike

Re: 440 six pack idle help [Re: DAYCLONA] #2752091
03/15/20 11:05 AM
03/15/20 11:05 AM
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Blair County,PA
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Originally Posted by DAYCLONA
It's hard to diagnose via the internet as we can't see or hear the operation of your set up, along with just the supplied info on hand, that being said I like to start with the basics to sometimes cover the most obvious often overlooked, you gave no mention of checking/setting fuel level in each bowl, to me this is the first operational/running step after confirming all mechanical installation procedures...


I'll mention this just for sh!ts and giggles: but I've come across 2 guys so far over the years that either daunted or unfamiliar with the set up, that have installed the center carb as delivered new from Holley, unfortunately Holley attaches and clips a hose from the PCV port to the bowl vent tube (why?), yeah the set up runs! (barely), but the PCV "vacuums" the bowl dry of fuel... it's simple problems like this that can cause some to render " complex solutions to simple problems", you/we need to know that all of the basics from installation to operational set up have been performed

Mike


And depending on whether you carbs original complete units or have been messed with or anything changed,I get more and more end carbs with center bows that have the accelerator pump passages filed with JB weld and used as end bowls.It will work "but" keep in mind the sight plug on the center bowl is 1/4" higher than the end,consequentially you have a 1/4" higher float level if you adjust float level as recommended and you are going to have problems.

Re: 440 six pack idle help [Re: Cab_Burge] #2752093
03/15/20 11:12 AM
03/15/20 11:12 AM
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[quote=Cab_Burge]I would test the power valve to make sure it is not ruptured or the gasket is leaking scope
I had a similar motor, 400 block bored to 4.375 with a 4.25 stroke crankshaft with 9.25 to 1 comp ratio with a comp Cams solid roller with 260@.050 on the intake lobes and 266 @.050 on the exhaust lobes, ground on a 108 LSA and installed 2 degrees advance so the intake lobe center was installed at 106 ATDC.
It had a low deck Eddy six pack intake with a set of OEM Holley 1970 440 6 pack carbs. with a 2.5 power valve, it would idle at 850 RPM in gear and 1000 RPM in neutral,it was a ton of fun to drive boogie
I did have to work on the carbs to get them to do that though, 1/2 turn out from bottomed out on the outboards mixture screws and right at 1.5 turns out on the center carb. No choke plate or bar in the center carb., the accelerator pump squirter was a #35 I think, I did use a screw with a nut on it in the return slot on the center carb to start opening the outboards sooner when I went to WOT, I had to try different locations on that but I think it was around 1/3 of the way from the top at idle in that slot. I did have a custom built 10 inch converter at first and later a 8 inch T/A SS race hemi converter that worked great on the street and at the track, way better than the 10 inch street and strip converter up
It will work great once you figure out what is currently wrong upscope wrench [/quote

The outer carbs screws are about 1/4 turned out and center is at 1-1/2 currently. I will try with a lower power valve at 3.5. Far as power valve or power valve bowl leaking, I did the pressure test and they are both good.

Re: 440 six pack idle help [Re: BSB67] #2752097
03/15/20 11:26 AM
03/15/20 11:26 AM
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Originally Posted by BSB67
If it idles better partially choked, you have a vacuum leak. Hand over the cab at idle to verify (choke fully open).

Any additional details on exactly what it does at idle without choke might be helpful info.

Make sure you have at least 25° ignition advance at idle.


I will try advancing to 25*, I don't think I tried advancing that far but will give it a shot. Far as the air leak is concerned, most people it talked to said the same thing that there is a leak. It is difficult to tell as the outer carb does take in some air naturally ( I could be wrong on this) but as I stated earlier, when I cover up the outer carb with a rag, it sputters and eventually dies. When I open the choke plate wide open while idling, I have to have my hand over the cab in order to keep the engine running.

Re: 440 six pack idle help [Re: Sixpak] #2752101
03/15/20 11:36 AM
03/15/20 11:36 AM
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Originally Posted by Sixpak
Start with the mixture screws on all 3 carbs out 1 1/2 turns.Put your finger over each air bleed and adjust the screw for that air bleed in or out so that when you cover the air bleed the idle does not change. Last one I set up ended up at 1 5/8 turns on all 6 mixture screws.

1 1/2 turn out for all 6 mixtures seems bit much I don't want to wash the cylinders out. I will try by turning them out another half turn and see what it does.

Re: 440 six pack idle help [Re: Tomkcuda] #2752105
03/15/20 11:45 AM
03/15/20 11:45 AM
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Monrovia, So-Cal, USA
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Sounds like a Vacuum leak or it is way to lean... Also recheck the float levels.... Are you running a low stall convertor also? That cold be an issue?


Bob(Cowboy)Hogan
Monrovia So-Cal
Re: 440 six pack idle help [Re: Tomkcuda] #2752111
03/15/20 12:05 PM
03/15/20 12:05 PM
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Originally Posted by Tom Kim
Originally Posted by Sixpak
Start with the mixture screws on all 3 carbs out 1 1/2 turns.Put your finger over each air bleed and adjust the screw for that air bleed in or out so that when you cover the air bleed the idle does not change. Last one I set up ended up at 1 5/8 turns on all 6 mixture screws.

1 1/2 turn out for all 6 mixtures seems bit much I don't want to wash the cylinders out. I will try by turning them out another half turn and see what it does.


It's not too much. And thats only the starting point. You adjust further by covering the air bleeds and turning the mixture screws in or out til you can cover an air bleed and the car's idle neither speeds up or slows down.. I read this info from Larry Shephard's 6 pak book years ago, and to me it also seemed like too much. But it was the thing that turned the corner for the 1st one I ever tuned. I thought I had jetting problems, a plugged center carb metering block, I thought I had to drill open the holes in the secondaries more, and none of it helped. But opening the mixture screws on the end carbs to be close to what the center carb wanted was the key. The car has to idle on all 3 carbs, and not just just a trickle out of the end carbs, either. Your nose and your eyes will tell you if its too much. So long as your floats are adjusted properly , 1 1/2 turns out on all 3 is the place to start tuning. Before you can adjust jetting, secondary diaphram springs, etc. it has to idle, and idle cleanly. It's counterintuitive, but it worked for me. If it were me I'd put the carbs all back to stock so I'd have a baseline and start there.

Re: 440 six pack idle help [Re: DAYCLONA] #2752115
03/15/20 12:08 PM
03/15/20 12:08 PM
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Originally Posted by DAYCLONA
It's hard to diagnose via the internet as we can't see or hear the operation of your set up, along with just the supplied info on hand, that being said I like to start with the basics to sometimes cover the most obvious often overlooked, you gave no mention of checking/setting fuel level in each bowl, to me this is the first operational/running step after confirming all mechanical installation procedures...


I'll mention this just for sh!ts and giggles: but I've come across 2 guys so far over the years that either daunted or unfamiliar with the set up, that have installed the center carb as delivered new from Holley, unfortunately Holley attaches and clips a hose from the PCV port to the bowl vent tube (why?), yeah the set up runs! (barely), but the PCV "vacuums" the bowl dry of fuel... it's simple problems like this that can cause some to render " complex solutions to simple problems", you/we need to know that all of the basics from installation to operational set up have been performed

Mike


Thanks Mike. I did fail to mention couple things. All 3 carbs are original 70's, the main body was slightly warped and was milled. There was a leak in the power valve bowl as it was not holding vacuum but since the milling, its holding vacuum now. The pcv port is located on the bottom. I will post a picture of the setup later this afternoon. I think I will also post a video and attach a link so all of you can better see my dilemma.
Far as the fuel level float is concerned I have messed with this many times. its currently set at half meaning basically fuel dribbling over the sight hole, if I lower the fuel level any farther, engine will not respond very well. I think I have this dialed in correctly.
One thing I was told to check was the fuel pressure. I am currently using mechanical Holley high volume 8 psi. Everything I read says use 6.5 fuel pressure regulator but does 1.5 pressure make that much difference?
Everyone I talked to says a vacuum leak somewhere.. One thing I have not triedis trying out a difference pcv valve. Could this cause too much air?

Last edited by Tom Kim; 03/15/20 12:14 PM.
Re: 440 six pack idle help [Re: racerhog] #2752137
03/15/20 01:26 PM
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Originally Posted by racerhog
Sounds like a Vacuum leak or it is way to lean... Also recheck the float levels.... Are you running a low stall convertor also? That cold be an issue?


Its a manual 4 speed and it stalls when I open the choke when its warmed up. I think float level is good but I am now second guessing potentially about the fuel pressure. I posted on a response to Mike that I have a mechanical fuel pump rated at 8psi. Not sure if 1.5 psi makes a difference.

Re: 440 six pack idle help [Re: Tomkcuda] #2752142
03/15/20 01:38 PM
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Thanks Everyone for you help so far
Here are the following things I will try based on your suggestions

1.. I will set the mixture screw on all 6 at 1.5 turn and adjust from there.
2.. I will exchange out 4.5 power valve to 3.5

3.. Different PCV valve.. perhaps current may not be the correct one.
4.. Advance timing to 25*

I wont be able to road test today as its raining heavy but will post with some photos today of the set up. I feel like I am close on this as it runs great with no bogging when I do WOT. Just issues of engine stall when choke is wide open at idle.

Re: 440 six pack idle help [Re: Tomkcuda] #2752146
03/15/20 01:50 PM
03/15/20 01:50 PM
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Originally Posted by Tom Kim
Originally Posted by DAYCLONA
It's hard to diagnose via the internet as we can't see or hear the operation of your set up, along with just the supplied info on hand, that being said I like to start with the basics to sometimes cover the most obvious often overlooked, you gave no mention of checking/setting fuel level in each bowl, to me this is the first operational/running step after confirming all mechanical installation procedures...


I'll mention this just for sh!ts and giggles: but I've come across 2 guys so far over the years that either daunted or unfamiliar with the set up, that have installed the center carb as delivered new from Holley, unfortunately Holley attaches and clips a hose from the PCV port to the bowl vent tube (why?), yeah the set up runs! (barely), but the PCV "vacuums" the bowl dry of fuel... it's simple problems like this that can cause some to render " complex solutions to simple problems", you/we need to know that all of the basics from installation to operational set up have been performed

Mike


Thanks Mike. I did fail to mention couple things. All 3 carbs are original 70's, the main body was slightly warped and was milled. There was a leak in the power valve bowl as it was not holding vacuum but since the milling, its holding vacuum now. The pcv port is located on the bottom. I will post a picture of the setup later this afternoon. I think I will also post a video and attach a link so all of you can better see my dilemma.
Far as the fuel level float is concerned I have messed with this many times. its currently set at half meaning basically fuel dribbling over the sight hole, if I lower the fuel level any farther, engine will not respond very well. I think I have this dialed in correctly.
One thing I was told to check was the fuel pressure. I am currently using mechanical Holley high volume 8 psi. Everything I read says use 6.5 fuel pressure regulator but does 1.5 pressure make that much difference?
Everyone I talked to says a vacuum leak somewhere.. One thing I have not triedis trying out a difference pcv valve. Could this cause too much air?


That duration cam of a will need a ton of initial advance. I would block the power valve if you suspest it, JUST TO GET THE IDLE RIGHT, DO NOT DRIVE!! It sounds like your outboards are a little rich at idle by your description, and the center is not doing much. The idle fuel feeds in the center metering block could be plugged. I have fixed a similar problem by finding a metering block that I can see the brass idle fuel bleeds in, so I can add more fuel, .001 at a time. Most stock 6bbl blocks have hidden feeds, so no dice there. 8 psi could overpower the floats, pull the sight plugs and see. The fact it will not idle without the choke tells me it is lean, meaning power valve ok, could be pcv valve, likely a mixture problem. Sometimes lean smells rich to most people. A few things to check
Front carb
.078 throttle blade holes
.055 idle air bleeds
#34 metering plate with .036 idle fuel bleeds .089-.089 jets
Rear is same with#35 plate .036 idle bleeds .086-.093 jets
Center .078 throttle plate holes
.068 idle air bleed
Make sure someone has not drilled any of those, and the metering plates are 6bbl #34-35, the new replacments are not the same.
Mine idles clean with an old .509 mopar cam, I know outdated junk, stock plates, 3/8 turn on the
outboards, 1-1/4 on the center, and those stock drill sizes I listed. 3.5 power valve, 64 jet and a 4-speed. If I go 1/2 turn on the ends it gets stinky. I need a choke to start it, none once it is warmed up. It will die if you turn 1 center mixture screw in, so it is close.



Re: 440 six pack idle help [Re: Tomkcuda] #2752147
03/15/20 01:50 PM
03/15/20 01:50 PM
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Originally Posted by Tom Kim
Thanks Everyone for you help so far
Here are the following things I will try based on your suggestions

1.. I will set the mixture screw on all 6 at 1.5 turn and adjust from there.
2.. I will exchange out 4.5 power valve to 3.5

3.. Different PCV valve.. perhaps current may not be the correct one.
4.. Advance timing to 25*

I wont be able to road test today as its raining heavy but will post with some photos today of the set up. I feel like I am close on this as it runs great with no bogging when I do WOT. Just issues of engine stall when choke is wide open at idle.

20200315_104217.jpg20200315_104139.jpg20200315_104122.jpg20200315_104101.jpg
Re: 440 six pack idle help [Re: Tomkcuda] #2752148
03/15/20 01:57 PM
03/15/20 01:57 PM
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Originally Posted by Tom Kim
Thanks Everyone for you help so far
Here are the following things I will try based on your suggestions

1.. I will set the mixture screw on all 6 at 1.5 turn and adjust from there.
2.. I will exchange out 4.5 power valve to 3.5

3.. Different PCV valve.. perhaps current may not be the correct one.
4.. Advance timing to 25*

I wont be able to road test today as its raining heavy but will post with some photos today of the set up. I feel like I am close on this as it runs great with no bogging when I do WOT. Just issues of engine stall when choke is wide open at idle.


Do not set the outboards to 1.5 out!!!! The way to do it is set the center to 1 turn, ends to 1/4-1/2, and adjust your idle fuel bleeds until it idles. My carbs sat on a 312/590 cam and did not need no 1.5 turns. The center should be 1-2 turns out, and 1 screw bottomed should kill the engine, with ANY holley, if the bleeds are right.

Last edited by 4406bbl; 03/15/20 01:59 PM.
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