Six Pack Issues.

[jimkov]

Recently bought a 71 Challenger 4 speed with a six pack. A couple times a drive I will accelerate and the RPMs will rise and then get stuck almost like on cruise control. The car does not have cruise control and if I put it in neutral and rev it then RPMs still won't drop below the sticking point. The only way I can get is to drops is re-engage the clutch and it will drop.

First post on this forum, thank you for the help!

 

[Daves69]

Hello. Welcome to the site.
More info on your six pack setup would be helpful.

FSMs are available for download ............

Service Manuals – MyMopar

mymopar.com

Youtube (Back 9) also has posted helpful videos such as......


Post some pictures of your setup as they may help remedy your issue.

 

[Xcudame]

And introduce yourself on the Welcome Wagon and include some pictures of your 71 Challenger!
There are several six-pack experts on the sight that help. First thing to look for is any linkage binding during full throttle operation. This can be checked without the engine running.

 

[jimkov]

Currently using a divorced choke. The six pack was added to a date correct 383. I am not sure where the six pack was sourced from. The engine has a mild cam and aluminum Ebelbrock performer heads. I have the divorced choke dialed to help compensate for the lower intake Temps.

 

[Steve340]

Could be the choke. My Edelbrock RPM heads had no exhaust cross over drilled.

 

[Daves69]

Think I'd start by making sure the cable itself does not bind at any point in its full travel.

Then I'd verify the bowl vent linkage isn't hanging on my air cleaner base causing interference..........

Next the throttle linkage return spring. I'd move the spring into the space between the cable end to keep it pulling in a straight line rather than an angle............

When adjusting the throttle cable, I loosen the cable retention nut and hold the throttle all the way forward making sure it's off the choke steps (green arrow bottom picture) and seated on the idle stop screw. Then I move the cable forward slightly to provide just bit of slack in the cable before securing the retention nut.......
Why is the choke rod not attached (red arrows, bottom picture)??

 

[jimkov]

Think I'd start by making sure the cable itself does not bind at any point in its full travel.

View attachment 130930

Then I'd verify the bowl vent linkage isn't hanging on my air cleaner base causing interference..........

View attachment 130927

Next the throttle linkage return spring. I'd move the spring into the space between the cable end to keep it pulling in a straight line rather than an angle............

View attachment 130928

When adjusting the throttle cable, I loosen the cable retention nut and hold the throttle all the way forward making sure it's off the choke steps (green arrow bottom picture) and seated on the idle stop screw. Then I move the cable forward slightly to provide just bit of slack in the cable before securing the retention nut.......
Why is the choke rod not attached (red arrows, bottom picture)??
View attachment 130929
View attachment 130931

Wow, thanks Daves69, I will start checking these recommendations out. These are photos from when I bought the car, the previous owner have the choke wired open. I hooked up the choke rod since then. But the rest of your points still have not been addressed.

 

[Ricks72Chlgr440]

Wow, thanks Daves69, I will start checking these recommendations out. These are photos from when I bought the car, the previous owner have the choke wired open. I hooked up the choke rod since then. But the rest of your points still have not been addressed.

In addition to Dave's recommendations; I would unhook the throttle cable and manually rotate the carb throttle shafts to see if there is any binding. The shafts should operate smoothly both opening and closing. The outboard carbs use a vacuum diaphragm under spring pressure which helps to close those carbs when air through those carbs stops flowing. There may be some resistance with those but the throttle shaft movement should still be smooth and they should close completely on their own due to that diaphragm spring.

 

[mrmopar340]

Move the return spring out. I think it is too close and hampering you idle down.

 

[6PKRTSE]

Disconnect the linkages to try to verify if it is one of the outboards or center carb by opening each one manually. If they do loosen the base plate bolts and re-tighten them evenly. If they were tightened unevenly it could distort the base plate just enough to cause it to slightly hang open.
The incorrect base plate gasket with too small of i.d. bores can also cause the butterflies to hang open.

 

[jimkov]

Disconnect the linkages to try to verify if it is one of the outboards or center carb by opening each one manually. If they do loosen the base plate bolts and re-tighten them evenly. If they were tightened unevenly it could distort the base plate just enough to cause it to slightly hang open.
The incorrect base plate gasket with too small of i.d. bores can also cause the butterflies to hang open.

Hey 6PKRTSE, I disconnected the linkage and the rear operates smooth but the front does get caught right before I fully closes. I have to click it shut by hand. I will loose the bolts for the plate and see if that helps.

I also straightened up the return spring and added some more tension. Thanks mrmopar340 and Daves69. Once I can get the forward butterfly smooth I'll take it for a ride. I have a feeling that might be it.

 

[jimkov]

So the issue is definitely the secondary not closing. The way the are set up now if I apply the slightest pressure one the linkage between the front the rear secondaries the RPMs increase about 300 rpm as stay stuck there until I apply pressure in the opposite direction to close them. When I apply the pressure I don't notice the front or rear butterflies exposing a gap but the RPMs do increase and stick.

Does anyone think my diagrams are bad or my vaccum is too low or possible my linkages are set up with too tight?

 

[Xcudame]

Disconnect the front and rear carburator leakage rods and see if there is any sloppiness in the butterfly shafts opening and closing. You want to make sure those shafts are still in a round hole and not an oblong hole. If the shafts don't wiggle around too much, I'd say it's a leakage adjustment. One of the unfortunate issues with our 50+ year old carburators is the butterfly shafts (steel) wear out the holes (aluminum). Luckily the carb can be machine for new bushings!

Also, check for wear in the area circled in red below where the two leakage rods attach. It looks a little worn to me.

 

[jimkov]

Fellas, thank you! Fixed the play in the linkage to make sure the butterflies fully sealed and I had my first enjoyable cruise without issue and got to feel the power or the 383 and six pack.

Problem solved!

 

[70iselin]

Nice write up on this, very informative and interesting

 

[Mopar426power]

My six pak issues are when the first one runs out and I have to go get another one.....

 

[Xcudame]

My six pak issues are when the first one runs out and I have to go get another one..

I cheat and buy two six packs or a 12 pack!

 

[6PKRTSE]

Drunks....