Possible Idea for Stalling Problem-77 New Yorker

77newyorker440

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I have been thinking quite a bit about my Chrysler's drivability problem, and after some time, I have come up with a few ideas. For context, it currently runs pretty good with the throttle open, but it has substantial off idle troubles, with stumbles and backfires. This is especially bad after warming it up. Here are my ideas:
1) Bad carb quality-I sent my Thermoquad to Dana to eliminate this issue as I know I can trust his work.
2) Fuel Pump-This issue never appeared until my mechanic replaced my fuel pump (old one was spraying fuel out the top). Perhaps not sending enough fuel? I would have done the job myself but I was scared of messing up and putting the car out of commission, yet it went out of commission anyway! Could also be a worn pushrod, I do not know how much lift is left in the current one.
3) Vapor Lock-Perhaps the fuel is getting too hot, leading to the lean backfires off idle?

Just some ideas, was wondering if anyone has experienced anything similar. Otherwise the car has been doing good, but I know it can run much better that it currently is. If none of this works, timing chain is next.
Thanks,
77newyorker440
 

Mike McGuire

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1. Timing
2. Vacuum leak
3. Logged float - (but the new carb should eliminate that one.)

Please report back what you discover.
 

Davea Lux

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Have you checked the timing chain for excessive wear? Ethanol blend fuels tend to create excessive carbon that can cause the EGR valve to stick open, this will cause rough idle and stalling in addition to very poor low end performance. If you have not done so already, you would want to consider installing a block off plate over the port for the EGR to see if that helps.

Dave
 

77newyorker440

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Timing is pegged at 14 degrees btdc, but a vacuum leak could definitely be present (I had about 16 inches of vacuum at idle), lots of dry-rotted vacuum hosing on the car. I checked the timing chain slack and it had about 6 degrees, but I have not pulled the cover to see if it jumped a tooth. EGR was blocked off when I installed headers on the car.
 

Big_John

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I have not pulled the cover to see if it jumped a tooth
If it had jumped a tooth, it wouldn't run. Still could be worn, but that's another story.
EGR was blocked off when I installed headers on the car.
And a little detail that makes a huge difference!

Headers will make the car run lean. You have a carb that's made to run lean to begin with, and some dry rotted hoses that might be causing vacuum leaks, now add headers on top of that and you can be running way too lean. This would explain why when the choke comes off (richer condition) the car starts to run bad.
 

77newyorker440

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Yes he did and he has the carb now to retune it after my mechanic messed up the carb and jud to be safe, I'll remind him about the headers, but that is a good point!
 

CBODY67

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Only issues when coming off-idle? Not at 1500rpm steady-state cruise and accel a bit? How much of the factory thermo-vacuum switches are still hooked up and working? To me, the off-idle situation tends to indicate that the throttle plates are either too far closed or too far open, which affects the use of the transition slots in the carb throttle bore. Too far closed, a flat-spot when the throttle is openned due to no/less transition fuel. Similar with too far open, which means that both the idle fuel feed system and the transition slots are feeding fuel to the motor at the same time. Too rich, usually, and a flat spot when the throttle is opened. If enough of the old vac hoses are cracked and adding air to the mix, closing the throttle plates more to compensate might be the reason for doing that. 16"Hg of manifold vac at idle sounds about right, all things considered. BUT replace the old vac lines BEFORE you get the carb back! Including the pcv line, too.

As you have headers on the car, what other changes have been made to the OEM production emissions hardware items? I know that, generally, one thing can lead to another and another and another, is the reason I'm wondering about this. Sometimes ending up sub-optimally. Just curious.

Do the timing chain as an investment in no further worries about it causing a problem later on, NOT to chase a drivability issue, from what I've seen over the years.

Just some thoughts,
CBODY67
 

Mike McGuire

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Since the car has headers, does it have the stock non-adjustable lifters, or have the heads been swapped?
Are their any other ignition or engine modifications?
 

77newyorker440

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Currently, the only power modifications it has are a deep sump Trans pan, headers, a mini starter, and a standard electronic ignition replacing the lean burn
 

77newyorker440

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Only issues when coming off-idle? Not at 1500rpm steady-state cruise and accel a bit? How much of the factory thermo-vacuum switches are still hooked up and working? To me, the off-idle situation tends to indicate that the throttle plates are either too far closed or too far open, which affects the use of the transition slots in the carb throttle bore. Too far closed, a flat-spot when the throttle is openned due to no/less transition fuel. Similar with too far open, which means that both the idle fuel feed system and the transition slots are feeding fuel to the motor at the same time. Too rich, usually, and a flat spot when the throttle is opened. If enough of the old vac hoses are cracked and adding air to the mix, closing the throttle plates more to compensate might be the reason for doing that. 16"Hg of manifold vac at idle sounds about right, all things considered. BUT replace the old vac lines BEFORE you get the carb back! Including the pcv line, too.

As you have headers on the car, what other changes have been made to the OEM production emissions hardware items? I know that, generally, one thing can lead to another and another and another, is the reason I'm wondering about this. Sometimes ending up sub-optimally. Just curious.

Do the timing chain as an investment in no further worries about it causing a problem later on, NOT to chase a drivability issue, from what I've seen over the years.

Just some thoughts,
CBODY67
I do not have a tach to tell you the exact rpms, but I feel the issue lies in around the 12-1300. I also feels that the idle is okay when in park, but when in gear, she is very lopey

One other change that should be mentioned is with the new exhaust, I have two cats as opposed to one, no mufflers
 

1970FuryConv

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I do not have a tach to tell you the exact rpms, but I feel the issue lies in around the 12-1300. I also feels that the idle is okay when in park, but when in gear, she is very lopey

One other change that should be mentioned is with the new exhaust, I have two cats as opposed to one, no mufflers
Damn. I bet that's a loud car. Nobody in the neighborhood stays asleep when you leave for work at 6am.:lol:
 
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CBODY67

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I do not have a tach to tell you the exact rpms, but I feel the issue lies in around the 12-1300. I also feels that the idle is okay when in park, but when in gear, she is very lopey
Thanks for the reply. As I recall, the factory-spec hot base idle speed should be about 700rpm in Park. I suggest you turn the idle screw DOWN approx 1/2 turn. adj the mixture screws, and see how that might work. At your guestimated idle speed in Park, the throttle plates are open too far. Probably goes into gear a bit hard, too, especially into Reverse when everything is up to operating temperature?

At the lower rpm, the restriction in the exhaust system (or lack thereof when compared to the stock system) would not be an issue in getting the carb to act right.

Enjoy!
CBODY67
 

77newyorker440

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Well, the tach I got from summit does not work at all, so that didn't help but I did discover that the connections on my ballast resistor were super loose, which might have contributed to the stumble. I plan on checking fuel pressure tonight and continuing to tinker while waiting for Dana to send my carb back. Still gotta figure out how to replace hazard/flasher switch as well, haven't doven into that job yet... Will keep you all updated.
Thanks for checking in,
77newyorker440
 

6PKRTSE

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Check or change the fuel pump push rod. I have had a couple over the years wear down enough that it would idle and somewhat cruise fine but upon any kind of acceleration it would pop and back fire lean.
 

Mike McGuire

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Double check your fuel filter and hoses/lines while you are at it. Cheap/easy to do.
Especially if there is a pin hole leak prior to the pump, you might hit pay dirt!
Good luck!
 

77newyorker440

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Hey guys, wanted to let you all know that I solved the problem!

Took it to see a friend of mine the other day and I told him the issue I was having, took him about 5 minutes to realize that I had connected my vacuum advance to ported vacuum, not manifold vacuum. I also had my brake booster rebuilt, as I noticed that it had a pretty severe vacuum leak. Now the car runs like a top, only a few small problems.

1) Headers keep burning up my #8 spark plug wire, trying new heat sock on wire that will hopefully fix that problem
2) Small vacuum leak under the dash, have not been able to find it yet, but it doesn't seem to affect driveability, still runs very smooth, able to balance a nickel on the motor at idle.
3) Clock stopped working...

Thank you all for the help, I greatly appreciate it!
 

CBODY67

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Vac advance should be attached to the ported vac port, not straight intake manifold vac, from the factory (PLUS a possibly deteriorated factory vac hose map, underhood). Reason is that ported vac lasts longer than intake manifold vac when you throttle into it. With full intake manifold vac, when you open the throttle quickly, no vac advance immediately. UNLESS . . . you get some of the vac delay valves which Ford was famous for using in the 1970s, put it inline (even two in parallel as GM did on a "factory fix") and turn them around backwards so it maintains vac in the vac advance can . . . which can cover for a very lazy dist mechanical advance curve.

Glad that the car is runing better.

Just some observations,
CBODY67
 
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