After 3 months of screwing around with the 6 BBL setup that was retrofit by previous owner, I finally gave up, yanked it off, and put on a Mopar Performance intake and a Holley Aluminum Street Avenger 770. Now it runs!
One of my previous threads described how it was runnning with the 6 BBL when I got it last fall. Missing at cruise, pinging during acceleration. But it was easy to start.
I pulled all the carbs, dismantled, cleaned, cleaned, and more cleaned (they weren't really visibly dirty), put in new gaskets, float valves, pump diaphragm, secondary diaphragms, idle air needle cork bushings.
Put it all on the car and couldn't get a high speed idle dialed in below around 2,500 rpm. Below that it would surge up and down about 700 rpm.
Blanked off the front and rear carbs and tried to go with just the center carb. Wouldn't start. Unblanked the rear, still no start. Unblanked the front, disconnected the choke rod and put fast idle to normal "warm" position. All throttles now fully closed. Starts, and "idles" at 3,000+ rpm, and won't come down.
Took everything apart, inspected, cleaned again, put it all back together, and same results. That's where I gave up.
Any carb buffs have any thoughts? I guess I could see if maybe the idle tubes in the center carb got clogged during cleaning that might account for not running on just the center unit. But the runanway idle on the front carb is a mystery. It takes a fair amount of air going in to run the engine over 3,000 rpm.
The 6 BBL setup is not for sale at this time
Deep-Sixed Barrel
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71_bronze_gtx
- GTX (RS)
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72 cuda repli-mod - Location: S. E. Michigan
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gcoupe72
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- My Cars: 1972 Road Runner originally equipped as lemon twist,400,4spd,air grabber,performance axle pkg.,bk. interior.
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Re: Deep-Sixed Barrel
Sorry to hear about your tuning problems.
The unsteady idle makes me wonder if you had tried disconnecting the vacuum advance.
Sometimes depending on the distributor,and/or the vacuum port you're using this can contribute to an idle that's a little too low, and when you try to increase it, it goes WAY up.
Your comments about the center carb may be correct. I think debris can get inside the metering block and block some of the very small internal tubes. The only access is through some small plugs on the ends.
Might not be a job for a first timer, check and see if one of the pro carb shops would do this for you.I've never priced a new metering block, but this might also be an option for you. Your 6barrel should run fine on the center carb, so that's probably where your problem lies.
And I'm assuming you've ruled out vacuum leaks in the intake, and between intake and heads.
Enjoy the car for now, but don't give up on the 6barrel, when you get it sorted, you'll love it!
The unsteady idle makes me wonder if you had tried disconnecting the vacuum advance.
Sometimes depending on the distributor,and/or the vacuum port you're using this can contribute to an idle that's a little too low, and when you try to increase it, it goes WAY up.
Your comments about the center carb may be correct. I think debris can get inside the metering block and block some of the very small internal tubes. The only access is through some small plugs on the ends.
Might not be a job for a first timer, check and see if one of the pro carb shops would do this for you.I've never priced a new metering block, but this might also be an option for you. Your 6barrel should run fine on the center carb, so that's probably where your problem lies.
And I'm assuming you've ruled out vacuum leaks in the intake, and between intake and heads.
Enjoy the car for now, but don't give up on the 6barrel, when you get it sorted, you'll love it!
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road chicken
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- Location: SE WI
Re: Deep-Sixed Barrel
I have litle real time with the 6pack setup but here's my .02c for what it's worth..
I agree with G, that wandering idle speed could be the vacuum advance , or even the mechanical advance if the springs are broken/ too light. I had that problem a couple of times with a 4 bbl with a vacuum leak. It would have to have the idle setting so far open it would start to get into the vacuum advance port, then zoom away it went to 3G.
Same for the center carb.
If you get the center carb handled and running right and it pings when you step into the outboard carbs , you may have to richen the outboard circuit- especially if your running in a 10% alcohol gas area. Have a freind of mine here witha 70 RT that had that problem and he had to richen the outboard carbs to get the mixture back in balance. Problem is the outboards do not have jets but a set orifice. Those can be opened up or a set of metering plates can do the trick. We did the plates because once the carbs are modified there is no going back.
good luck
I agree with G, that wandering idle speed could be the vacuum advance , or even the mechanical advance if the springs are broken/ too light. I had that problem a couple of times with a 4 bbl with a vacuum leak. It would have to have the idle setting so far open it would start to get into the vacuum advance port, then zoom away it went to 3G.
Same for the center carb.
If you get the center carb handled and running right and it pings when you step into the outboard carbs , you may have to richen the outboard circuit- especially if your running in a 10% alcohol gas area. Have a freind of mine here witha 70 RT that had that problem and he had to richen the outboard carbs to get the mixture back in balance. Problem is the outboards do not have jets but a set orifice. Those can be opened up or a set of metering plates can do the trick. We did the plates because once the carbs are modified there is no going back.
good luck
4th generation B bodys- there is no substitute.
68 383, Street Demon 750, RPM top end,484/284/108 poo poo cam "-5 spd 4:10 SG, 4whl disk, Helwig Anti-Sway, Poly bushings,Firm Feel Box, HD Linkage, 1" t-bars, 7 leafs Springs
68 383, Street Demon 750, RPM top end,484/284/108 poo poo cam "-5 spd 4:10 SG, 4whl disk, Helwig Anti-Sway, Poly bushings,Firm Feel Box, HD Linkage, 1" t-bars, 7 leafs Springs
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71_bronze_gtx
- GTX (RS)
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- My Cars: 71 GTX
72 cuda repli-mod - Location: S. E. Michigan
Re: Deep-Sixed Barrel
I left a lot out to keep it short.
I did disconnect the vacuum advance and plug the line. That stopped the unstable rpm. (the distributor vac. advance adjustment was full CCW when I got the car. That disables any vacuum advance. I set it full CW since I have such low vacuum. That was too far. Tried to bring it back but found the .050" hex socket was stripped due to rust. Bought a reman distributor.) But still unable to get it below 3,000 once the front carb was "unmasked". Could not spot any air leak in the front carb.
I am aware of the goodies Promax sells for six-packs to make them tunable and user-friendly.
Someday, maybe I'll send the carbs to Holley for restoration...............
I did disconnect the vacuum advance and plug the line. That stopped the unstable rpm. (the distributor vac. advance adjustment was full CCW when I got the car. That disables any vacuum advance. I set it full CW since I have such low vacuum. That was too far. Tried to bring it back but found the .050" hex socket was stripped due to rust. Bought a reman distributor.) But still unable to get it below 3,000 once the front carb was "unmasked". Could not spot any air leak in the front carb.
I am aware of the goodies Promax sells for six-packs to make them tunable and user-friendly.
Someday, maybe I'll send the carbs to Holley for restoration...............
Re: Deep-Sixed Barrel
Check out the Six Pack how to guide posted by Tom Quad in this Moparts thread link here :
http://board.moparts.org/ubbthreads/sho ... ost6110103
http://board.moparts.org/ubbthreads/sho ... ost6110103