TUNING A SIX PACK

mac

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How was the quality of your new replacement base plates from Holley? I got a set to replace my original 69 carb plates. I was so disappointed in the quality. I'm still using the originals and set the new Holley plates in my spare Holley parts bin. This was probable 2010-ish

the carbs i had were pretty rough and just about anything would be an improvement. also, like i mentioned before, i did not have a good experience with the Promax replacement.
 

440beep

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do you by chance have a photo of these small screws? I'm trying to visualize................

Sorry, stock end carb baseplates have the small screw under the baseplate. This will adjust the blade position at idle. A slight change can make a big difference in idle quality and transition response.
Pulling the plugs for the end carb mixture screws is important too, a small change 1/4 turn or so makes a really big change in the idle quality. In the '70's these changes were not widely known, which is why I could buy used 6 Pacs for such low prices at the time. Many stock 6 Paks did not run well on the street. Small changes made amazing improvement.
 

66Satellite47

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do you by chance have a photo of these small screws? I'm trying to visualize................
No my 6 Pak's are long gone. If you look under the base plate on the end carbs you can see the screw that sets the throttle blade position. You need to have the end carbs off to see it.
 

66Satellite47

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So you are saying i am better of putting back the 6.5 valve ?
Thank you.
Zoi

As you look through this thread you can see that 6 Pak's need a lot of tuning attention to run real good. The power valve should not have a real big factor at idle. Try a few. But start with the basics. Float level, idle mixture screws, main jet size. On most stock combinations the end carbs are lean, maybe not yours. Many 6 Pak's got modified back in the day, look to see if yours is one.
 

MAPS

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Thanks I have done everthing and twice.
My last bet is sending them out to some guy everyone swears by and see what happens there and if that is not succesful ...4 "pack"
here I come...lol
 

RJRENTON

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Thanks I have done everthing and twice.
My last bet is sending them out to some guy everyone swears by and see what happens there and if that is not succesful ...4 "pack"
here I come...lol
If you do not get your problem fixed and proceed with your "4 pack conversion", I'll give your old carbs s good home.....
BOB RENTON
 

66Satellite47

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Thanks I have done everthing and twice.
My last bet is sending them out to some guy everyone swears by and see what happens there and if that is not succesful ...4 "pack"
here I come...lol

Which intake are you using, and which carbs? The '69, 70 & 71 carbs seemed to be very different in what they wanted.
A 4BBL will likely take some work too. I spent over two months and at least 100 runs to get my 850DP and TM7 intake dialed in. No instrumentation, computers and O2 sensors back then.
 

BrianInTexas

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Is there anyone in south/central Texas (I’m about 65 miles west of Houston) with six pack experience that can help me dial in my car? I can adjust fuel levels in the bowls and adjust idle mixture, but I have only a little experience (rebuilt a 4 bbl and changed power valves) beyond that with fine-tuning carburetors, and no experience with six packs. My car was running well and then spark plugs fouled…I believe the front or rear carb float/needle/seat stuck open and started flooding the engine. I changed the spark plugs, checked the bowls/floats and plan to get some clear bowl plugs to set the fuel level as described in this post. However, for me to go beyond that, I’m more likely to make things worse, or as Clint Eastwood said, “man has got to know his limitations.” I’m also open to trailering my car to someone that can help. Of course, I expect to pay for this and hopefully make some new friends along the way. Thanks, and I’ll post updates after I experiment with getting the fuel level correct in the bowls. Brian
 

66Satellite47

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You do need to get the float levels correct. If needed replace the needle/seats. Stock jetting is probably pretty close. I found that on the end carbs, taking the end carb idle mixture screw plugs out and richening them slightly 1/8 or 1/4 turn made a big difference. Also on the end carbs the idle throttle position has an adjustment screw below the baseplate. I found that that helped, but I had a pretty big cam.
 

BrianInTexas

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You do need to get the float levels correct. If needed replace the needle/seats. Stock jetting is probably pretty close. I found that on the end carbs, taking the end carb idle mixture screw plugs out and richening them slightly 1/8 or 1/4 turn made a big difference. Also on the end carbs the idle throttle position has an adjustment screw below the baseplate. I found that that helped, but I had a pretty big cam.
Thanks for the suggestions…I’m going to start with the floats and go from there.
 

AAR4Fun

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the power valve has absolutely no effect on the idle whether it’s closed or open. The reason for the high number is the engine pulls extremely good vacuum once it’s going down the road. I have the jetting as such that it cruises high 13’s to low 14’s depending on the speed. Exactly where I want it. When you throttle it to accelerate with the current jetting it needs the enrichment from the PV to keep the A/F from going lean. I found the 10.5 to be ideal as the vacuum only drops to about 9” when I accelerate (moderately without getting into the secondaries). When I had a lower number PV in it I got absolutely no enrichment from the circuit. So I upped it to take advantage of the circuit. Pvcr is opened up to 0.76. This is a bigger center than stock. It’s a 4412 which is essentially the front half of a 750.
I know this post is sometime back in the thread, but need to know. Were you experiencing any stumble or falter with the lower PV while the pedal is in motion and before secondaries come on? My AFR leans from mid 14's to 16's before more fuel is introduced and it comes back down. This is with only the center carb functional.
 
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Frustration

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OK, here's a little update. Last night I bucked up and took my road runner to the local chassis dyno. I'm trying to get the car ready for a track rental Memorial Day Weekend where lots of my buddies will be fighting for the top of the hill honors. My main goal for this session wasn't necessarily to get optimum HP and TQ, but rather to be sure my air/fuel metering was good and that I wouldn't lean it out up top. I made four full pulls and one half pull due to a lean condition. In the beginning the car was lean through the entire pull and made just 400 HP to the wheels. After a lot of changes to the outboard carbs, the lean condition didn't seem to go away much, if at all. For the final pull, I upped the jets in the center carb to #84's. The front carb had #85's, and the rear #86's. I ran a #28 squirter in the center carb. On the final pull, the lean condition existed between 4200-4800RPM, then went to 12.9 for the rest of the pull to 6500 RPM. What we think we found out is this: The lean condition is likely due to an incorrect power valve in the center carb. I do not see any numbers on the valve, and have no info to tell me what it is. After work, I plan to warm up the car and check the vacuum while in gear. I'll purchase new power valves to test at the track in a little over a week. The final changes netted a peak of 426 HP and 411 TQ. Peak HP is at 5600 RPM, but it's pretty flat up to the 6500 RPM shut off point. At this time the best ET on the car is 11.04, and the best MPH is 122.84, but they were not on the same pass. It hasn't run over 120 MPH in quite a while. Fingers crossed it will hit the magical 10.99, and will hold off the competition next week. If all else fails, I'll probably uncork the headers to hit the mark. More to come in a little over a week!
Sorry for the delay getting back to this bogging off the line, and lean condition in the 4000 RPM range. I noticed a fuel leak on my intake manifold. Not a ton, but enough to smell and a small puddle would form on the driver's side. I found out that the accelerator pump had warped due to someone (probably me) overtightening it. I put a straight edge on it, and it was considerably bowed. I used a fine file and brought it back to square. It solved the leak as well as the bog down low. It was actually pumping gas out between the accelerator pump and the carb base. It was enough to see when I took the air cleaner off. May be worth checking if you have an old set of carbs.
 

68 HEMI GTS

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I know this post is sometime back in the thread, but need to know. Were you experiencing any stumble or falter with the lower PV while the pedal is in motion and before secondaries come on? My AFR leans from mid 14's to 16's before more fuel is introduced and it comes back down. This is with only the center carb functional.

I could see it on the A/F gauge, it felt slightly smoother with the higher number PV as well when you accelerate from a roll. Keep in mind if your vacuum outboards start to open you will see a lean spike untill the boosters turn on. No way around it.
 

Frustration

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Here's a little update on a change I made yesterday. I was able to borrow back my old Weiand six pack, tunnel ram from a close friend. This intake has all the Mopar Engine Book modifications to the inside, including dams and grinding, as well as a jet change to my stock carbs per the book. When I started the car, it seemed to have a vacuum leak. I took the intake back off and re-sealed it with new gaskets. Upon startup, it did the same thing. I started to play with the air/fuel mix and that cleaned it right up. It wanted at least two turns on the center and 1 1/2 on the outboards. At that point, it ran near perfectly. I took it for a ride and was pleasantly surprised with the road manners, though it did change the note of the engine in a positive way. Once warmed up, I matted the throttle at around 45 MPH while in high gear. The car fell over for a second or two, then took off like a banshee! Thinking further, I never changed from the soft, yellow springs in my outboard carbs. I'm guessing they opened the secondary carbs too soon, and there was not enough fuel to support all the air. I also have the same squirter in the center carb. Today I plan to change springs and squirter before our cruise. On a side note, I took the car to my buddy's house to show off the cool intake. A few of my friends were standing around the engine bay, admiring it and asked to start it up. I told another buddy to reach in and hit the key. With no throttle action at all, it fired up and idled like a stocker. To say I'm pleased would be a gross understatement! One final note...further back in this thread, a question was asked whether this intake setup would fit under the stock, lift-off hood. It does, but not without modification to the air cleaner base. I ran the car without an air cleaner as I don't want to cut my original base. I run a reproduction hood that is very close to the original style, including the part under the scoop where the air cleaner seals to the hood. That is where the air cleaner hits. I used to run a cheap aftermarket hood that had a much larger opening under the scoop. That hood cleared the air cleaner in stock condition. (this is not the A12-style base, but the other, oval style. The A12 base will not work) I hope this bit of info helps others as this intake is one of the coolest I've ever laid eyes on. Good luck my friends!
 

68 HEMI GTS

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Here's a little update on a change I made yesterday. I was able to borrow back my old Weiand six pack, tunnel ram from a close friend. This intake has all the Mopar Engine Book modifications to the inside, including dams and grinding, as well as a jet change to my stock carbs per the book. When I started the car, it seemed to have a vacuum leak. I took the intake back off and re-sealed it with new gaskets. Upon startup, it did the same thing. I started to play with the air/fuel mix and that cleaned it right up. It wanted at least two turns on the center and 1 1/2 on the outboards. At that point, it ran near perfectly. I took it for a ride and was pleasantly surprised with the road manners, though it did change the note of the engine in a positive way. Once warmed up, I matted the throttle at around 45 MPH while in high gear. The car fell over for a second or two, then took off like a banshee! Thinking further, I never changed from the soft, yellow springs in my outboard carbs. I'm guessing they opened the secondary carbs too soon, and there was not enough fuel to support all the air. I also have the same squirter in the center carb. Today I plan to change springs and squirter before our cruise. On a side note, I took the car to my buddy's house to show off the cool intake. A few of my friends were standing around the engine bay, admiring it and asked to start it up. I told another buddy to reach in and hit the key. With no throttle action at all, it fired up and idled like a stocker. To say I'm pleased would be a gross understatement! One final note...further back in this thread, a question was asked whether this intake setup would fit under the stock, lift-off hood. It does, but not without modification to the air cleaner base. I ran the car without an air cleaner as I don't want to cut my original base. I run a reproduction hood that is very close to the original style, including the part under the scoop where the air cleaner seals to the hood. That is where the air cleaner hits. I used to run a cheap aftermarket hood that had a much larger opening under the scoop. That hood cleared the air cleaner in stock condition. (this is not the A12-style base, but the other, oval style. The A12 base will not work) I hope this bit of info helps others as this intake is one of the coolest I've ever laid eyes on. Good luck my friends!

sounds like it works pretty good. I’d consider modifying the stock intake If you go back. I worked the dividers down a bit on mine. I picked this mod up from a guy with a really good running six pack stroker. It seemed to strigten up some of the low speed manors and it flat screams at WOT. Then I seen a very similar mod on a dyno test on YouTube the other day.
8716D307-C9A9-4C24-A1B7-45D60B171B7F.jpeg
B6836604-18E4-4E63-BBCA-1821BB8F9EE7.jpeg



 

Frustration

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That's really cool. Would love to know how much difference the mods to the intake made. I'm sticking with the Weiand for a while anyway. I may do the stocker mods though, while it's off the car. Thank you for posting.
 

68 HEMI GTS

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That's really cool. Would love to know how much difference the mods to the intake made. I'm sticking with the Weiand for a while anyway. I may do the stocker mods though, while it's off the car. Thank you for posting.

I don’t have any track data with the modified six pack or the mechanical carbs for that matter. It feels quicker than when it made the 10.90 passes. Although I’m putting a 4 speed in the car so I’ll never really get a true good test. The guy who I stole the intake mods from had a 12:1 TF240 headed 512 in a full steel 70 bee running 10.40’s. That helped make up my mind to try it. He was kind enough to share some really good pics of the mods. His manifold was ported by MCH. Same car but slower dial as it had iron heads in the pic. Real V code as well!

C0D919F8-3DBC-4793-B66E-3B8A5EB5AF4F.jpeg
 

biomedtechguy

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A few quick notes on a great thread.
DON'T LEAVE CLEAR PLASTIC fuel bowl site plugs in any longer than needed to adjust the float level! They rapidly get soft and melt. I know from personal experience.
I have a beautiful example of the Weiand P3690982 6bbl intake, after researching it more than any sane person should. The only mods on mine are the sharp 90° angles where the plenum floor meets the intake runners have been beautifully radiused, one of the recommended mods in the Chrysler Performance tech bulletin. There are mods a guy "6BBL FLASH" did that are shown on the Victory Library site and he raced regularly, and got about 2/10ths faster times than the Chrysler Performance mods got him.
Also, I was REALLY disappointed that the Weiand wouldn't fit under my 70 Roadrunner N96 hood, but as part of my research, as stated above, it will fit under the aftermarket, slightly larger A12 6bbl hood scoop.
Paul Rossi said that intake was done at 6,500 RPMs, and another guy Jed who has a YouTube channel had 3 home built 500 cfm 2bbl carbs on a Weiand, well set up, and he has decided to go to a 2x4bbl setup because of the same reason, his cam and 500 cu in stroker need more RPM capability than the Weiand can offer.
I may never use mine, as I have a Bill Mitchell aluminum RB block that I'm building into a 541 stroker, and I can't see using TF 240 heads on a 541, so I'm going with the TF 270 Max Wedge port size heads, and in an attempt to keep it under my Air Grabber, I'm using the Indy ModMan intake CNC'd to MW port size.
 

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