6 Pack Carbs....when should secondaries open?

[wsr1961]

First, I know very little, so a hi tech answer will be over my head. I notice that the secondaries are linked to a cam by the main throttle. When I move it back and forth, the secondary linkages do not move. I see that there appear to be vacuum devices on the other side of the shafts on the secondaries. It looks like those diaphragms would cause the secondaries to open, as the other connection via linkage to the main throttle seems passive.


If I crank the car and accelerate by manipulating the main throttle by hand at the center carb, the secondaries just sit there. The linkages do not advance and open them.

I have a lot of gas coming out the exhaust. My suspicion is that the secondaries are not letting any air in.

Any ideas? Should the secondaries open when I move the main throttle linkage, or are they controlled via diaphragms on the other side? If so, what triggers the diaphragms to open the secondaries?

 

[74 challenger]

A pic would help to see if the vac lines are hooked up correctly and linkage. . My out boards opened I believe around 1200 rpms. Are they new,old and did you change the springs on the out boards? Did you just install them for the first time? Need more info.

 

[704406]

Yes more info and pictures will help tell us if the carbs are relatively stock or not. If they are stock, the secondaries are only opened by vacuum created by the centre carb, and the secondary carb's opening is controlled by the springs in the vacuum pots on the outboard carbs. The linkage is only to close the throttle on the outboard carbs, not open them.
There was an aftermarket manual throttle linkage kit available but it's not advisable for daily use on the street.
If it seems that it's running "rich" check the float height it is quite critical that it be correct.
If the carbs have been sitting a while the gaskets could be dry and shrunk, which can cause flooding problems, or the needle and seat "o ring" can be cracked or dry and not sealing the fuel in the bowl, both can cause the engine to run "rich"
What engine are you running, 340 or 440?

 

[dadeo1852]

Assuming it's stock and looks like this, the vacuum lines I marked in yellow provide the signal to open the frt & rr carbs from the center carb just like 7044406 says. If you got raw gas coming out your exhaust then definitely something wrong most likely with floats stuck or out of adjustment assuming no ignition problems.

 

[wsr1961]

I have several pics of six pack set ups. I think the only difference in mine and the typical 440 set up is the port for vacuum advance is plugged and the vacuum advance on the distributor is connected to the master cylinder. The car is a 1971 440 6 pack clone, and the only thing I have done is add a stronger alternator and modern dashboard instruments with a retro look. Here is the history, as I know it:

The engine has a '74 block, A '70 six pack intake manifold, period correct carbs, Edelbrock Performance RPM aluminum heads and ceramic headers. It also has a Be Cool electric fan and radiator system. I was told it has a strong cam, and I believe it.

When I first got it, it ran good but didn't seem to have much power. The battery, which is in the trunk, would also discharge slowly, leaving me needing a jump start after about 30 minutes of driving.

I put the car through two shops. The first added the modern gauges and claimed to correct the power drain. They didn't. The car still had a 9 second 0-60, and the battery still drained when I drove it.

The second shop said that the throttle cable was somehow binding, and that they were able to fix that and get the power up. They also installed a stronger alternator, thinking the electric fan and electric fule pump, plus modern gauges were pulling too much power. The engine definitely produced more power when I picked the car up from shop #2.

I figured out that the battery was still not charging when I drove it. I have a new battery, alternator and voltage regulator. A voltmeter shows no drop in power between the alternator and battery, so I believe the connection is good. The car was idling at about 600 RPM. I turned the idle screw and increased idle to about 900 RPM, and the alternator seemed to spin fast enough to keep the battery charged at idle. But when I drove it, it was backfiring constantly in the exhaust when I accelerated.

At that point, I started playing with the timing. I thought I could advance the timing to burn more fuel and get rid of the backfire and the gassy smelling exhaust. But what I have done is adjust it so that the engine is sluggish again, but is not backfiring. I still get gas smelling exhaust. The electrical system will charge the battery at idle. It just seems as though I can either keep the battery charged or have the engine putting out maximum power, but not both. And I am a total idiot when it comes to these adjustments.

 

[rklein71]

Make sure your ignition is working correctly including a solid ground from the engine to the frame and the ignition module to the firewall. I am assuming you have Mopar electronic ignition. With any electronic ignition, a poor ground will lead to a weak spark which will cause tuning headaches including poor burning of fuel resulting in a rich exhaust mixture (unburned fuel). This happened to me and once I got the ignition fixed, tuning my six pack was easy. Rod

 

[aussiemark]

Your outboard carbs are vacuum operated and if the car is sitting there idling and you rev the engine you won't develop enough vacuum to see any movement the car's engine needs to be under load, on a dyno you'd see them open.

 

[aussiemark]

It is hard to find mechanics that know how to correctly adjust carburettors these days because it is not part of their training and hasn't been for many years. Start the engine let it idle for a moment then switch it off now on the centre carb open the choke blade by hand (not the throttle blade) and with a flashlight check and see if fuel is drooling out and building up on the closed throttle blade. Then check the outboard carbs (no need to open the choke because there isn't any) for any fuel drooling out and building up on the throttle blades.

 

[Daves69]

............
The 6 Bbl tips

Also check the "7 pages" of links for more.

 

[Chryco Psycho]

I agree that it is tough to find anyone who knows how to tune these , I have Only tuned about 25 of the 6 packs over the years & I am almost 60 , if you were factory trained & good at it you might have been 25 years old in 1970 , do the math !!
As above you will not get enough vacuum in the venturii of the center carb to open the secondaries without a load on the engine , with higher stall converters & low rear gears you can use lighter springs & get the secondaries to open sooner / lower rpm , but they should start to open around 2400 rpm & you will hear them !! .
The vacuum advance also needs ported vacuum , you have it connected to manifold vacuum which will give you vacuum retard as you will have full advance at idle & it will decrease as the vacuum drop with rpm , no wonder you cannot set the timing , disconnecting the vacuum advance would give you a better result LOL , I would set the timing at 14* at idle with a 20* curve so you are at 34-35* above 2500 rpm & leave the vacuum advance off . You cannot reverse the vacuum connecting on the center carb , the lower tube is for the secondaries , the upper for dist advance !
If you think of the 6 pack as a 4 bbl with a huge secondary it will simplify things , as this is the way it operates .
work through the basics , set the float levels properly , set the idle mixture screws while warm , check the engine manifold vacuum idling in gear & make sure you have more than 7" if not you need to change the power valve to a lower opening rating .
when tuning properly these work extremely well .
I am willing to help you work through tuning it correctly .

You also Must install a 10 ga wire from the alt output to the battery post on the start relay as you now have far too much load through the firewall connections & ammeter gauge in the dash . the reason you were discharging is you have more amps drawing from the battery than the alt can produce to charge the battery. Do Nto delay , add the bypass wire immediatley

 

[wsr1961]

Chryco, can you walk me through the process somehow? In all honesty, I don't understand a lot of the terms you used. I am a rookie.

I do have a wire running from alt to starter.....sort of. It runs to the fender, where it is bolted down with several other wires. One of those wires runs down to the starter. Another wire bolted to the starter then runs back to the battery positive post in the trunk. I have checked voltage and there is very little drop off from alt to battery and starter.

As to the carbs, I don't even know what the things you are telling me to adjust and/or check are. I'm reasonably intelligent, but untrained. I have money, if I need to buy gauges to measure vacuum, etc.

 

[Chryco Psycho]

Send a pm with a phone # , I can discuss this faster than typing it all out !!
I should be able to call around 7:30 pm tomorrow or suggest another time that works for you

 

[wsr1961]

You should have pm. That time is fine, and thanks.

 

[Chryco Psycho]

Any updates or progress ??