Slowly....dying...

[Jam72]

My car starts out it's drive pretty well, but then the more I drive, the lower the idle gets... then the car acts like it wants to die. Putting it into neutral and resting my foot on the gas pedal seems to help a bit. This is after just a few minutes of driving. Other symptoms that may or may not be related:
1. Speedometer intermittently bounces to +20-30mph and back, getting worse the faster I go. On the freeway, it spins waaaaay past 100mph and back, super fast. It's kinda funny but not.
2. Voltage gauge seems to read a bit lower than I remember. When I shut the lights off, it jumps to +20 for a sec, then back to what you see in the pick below. That seems normal-ish, I guess as demand on alternator is suddenly reduced.

I've driven, worked on, and built a ton of cars, but never worked on anything this old, so I post silly things because I'm not familiar with what systems of these cars are related/dependent on each other.

Ideas? Do I run a voltage check from the post on the back of the alternator? At the battery? If I need an alternator, how do I know which I need (I do NOT trust my local auto parts store)? I think I've read there are single and double post. Internal and external regulators? Sheesh, old cars LOL. I'm spoiled and used to just buying the ONE part that fits my cars...

Thanks, in advance!

My voltage gauge at idle and while driving:

View attachment 1574826

Years ago I have had to replace Speedo cable due to the square end rounding off. It will cause the symptoms u describe sometimes skipping a revolution. An easy change with any original or after market cable as long as it is the correct length. The idling problems are much more complex to pin down. I once had a Ford that would act up when warmed up. It was the coil which seemed to act up with winding wire opening with heat. May be a long shot but easy to replace. Fuel issues are more complex. A check of vacuum lines may be worthwhile as well.

 

[Jam72]

The car doesn't run any better after being off for a few mins. When I park it and come back out, it's the same.


Update: So far, I've tossed in the new plugs and blew air through the idle circuits. It may be doing marginally better. I then made sure the idle was at a solid 850 (A/T trans).
The car still stumbles while tipping in throttle but does great when I punch it LOL. I don't like the car stumbling as I'm trying to pull into traffic like a normal person, though. This is the exact same thing my Holley did and why I got rid of it.
I verified the choke and it's completely open once warm.
Also, I am now seeing the idle hunt a but while in drive and at a stop. Maybe it's been doing this the entire time and I just didn't notice. Not like vacuum leaks that I'm used to, though. This is much slower. In gear, the idle drops to about 700ish (I wasn't wearing my glasses LOL) then, after about 5sec, will drop a bit for 3-5sec then back up. Repeats.
So... maybe the car has developed a vacuum leak, though the carb is new, installed just a few miles ago, and all vacuum lines are new AAAAAAND the car ran perfectly just a couple weeks ago.
I thought carbureted cars were supposed to be simpler than newer stuff? On the bright side, there's only three vacuum spots to check. If no luck, I'll pull the carb and try a new gaskets between the intake, heat shield, and carb. If still no luck... then I don't know. ....

Carbureted simpler? Not in my experience.

 

[kaj750]

Carbureted simpler? Not in my experience.

Learning that the hard way. I miss being able to dialogue stuff until exactly where the problem is.

 

[pedal2themetal]

HI,
have you adjusted the air/fuel mixture screws? starting at 1 1/2 turns out from lightly seated, then when warmed up adjust them evenly in/out to heights vacuum.
What about timing? when watching it at idle does it move around to where you don't see it with every flash of the light? if it does the timing chain is bad..

good luck take care be safe
tim

 

[Sparky Anderson]

Seriously? You believe there is more experience/knowledge on that YouTube channel than there is here? The combined experience of the handful of members who have already responded to this thread alone far out paces that guy. Heed the training/experience disclaimers he adds to each one of his videos.

Well he may not be giving all the info. Don't want to steer him in the wrong direction. That guy I am referring to works on alot
if different mopars, has more experience than you think. Happy New Year to you and your family and all the best in 2024.

 

[kaj750]

HI,
have you adjusted the air/fuel mixture screws? starting at 1 1/2 turns out from lightly seated, then when warmed up adjust them evenly in/out to heights vacuum.
What about timing? when watching it at idle does it move around to where you don't see it with every flash of the light? if it does the timing chain is bad..

good luck take care be safe
tim

It's been a while since I checked the timing but I probably should.
I *think* the painted mark on the pulley is the right one and that the timing is in spec. Car doesn't donate. Seems to run fine though it could possibly use more advance, based on how it heats up in the summer and occasionally diesels when turning off.
I'm so out of practice on tuning cars with carburetors and distributors.
I'm kicking myself for not keeping up with it. I honestly never thought I'd be able to afford my dream car though.
But, here I am.
First world problems LOL.

 

[pedal2themetal]

HI,
Is the idle still 850 or higher?? that could cause the dieseling in summer. Idle needs to be 650 rpms...
You need to find the right mark on the crank.. Pull the #1 plug and put a straw in the hole and watch it while you rotate the motor by hand and see where it stops moving out of the hole , that would be TDC of the piston (Now the distributor won't necessarily be pointing to #1)..look and see what mark is at 0*.

good luck take care be safe
tim

 

[kaj750]

HI,
Is the idle still 850 or higher?? that could cause the dieseling in summer. Idle needs to be 650 rpms...
You need to find the right mark on the crank.. Pull the #1 plug and put a straw in the hole and watch it while you rotate the motor by hand and see where it stops moving out of the hole , that would be TDC of the piston (Now the distributor won't necessarily be pointing to #1)..look and see what mark is at 0*.

good luck take care be safe
tim

Yes, 850 but I'm in Winter months now. If I set idle to 650, the car barely keeps running when in gear and stopped. Lights flicker, and it just about dies. Torque converter is unlocked, best I can tell.
Straw. Check.

 

[pedal2themetal]

HI,
Have you tried adjusting the mixture screws when you've had the idle at 650?? at 850 your above the idle circuit and they most likely do nothing. adjust them evenly 1 1/2 turns out from lightly seated then to adjust turn in/out 1/8 to 1/4 turn at at time to smoothest idle. they ONLY effect idle quality and if not adjusted properly will cause it to not want to idle at proper rpm...
Once you get the idle you well have to re-time it .. trying to time it at a higher rpm is throwing it way out of wack especially at higher rpm's..
Just realized you have an automatic, Idle speed for an automatic is 750,,

good luck take care be safe
tim

 

[kaj750]

HI,
Have you tried adjusting the mixture screws when you've had the idle at 650?? at 850 your above the idle circuit and they most likely do nothing. adjust them evenly 1 1/2 turns out from lightly seated then to adjust turn in/out 1/8 to 1/4 turn at at time to smoothest idle. they ONLY effect idle quality and if not adjusted properly will cause it to not want to idle at proper rpm...
Once you get the idle you well have to re-time it .. trying to time it at a higher rpm is throwing it way out of wack especially at higher rpm's..
Just realized you have an automatic, Idle speed for an automatic is 750,,

good luck take care be safe
tim

Okay. I was advised 850 at idle which could be throwing everything off.
I'll set to 650 and start over on everything.
I should have time this weekend.
Thank you!
FWIW, I tried to find someone in my area to either do all of this for me or teach me how. Apparently it is so much work that nobody was willing to do it for any price lol

 

[pedal2themetal]

HI,
Yes there's not many of us left that know anything about the older auto's.
Oh and actually the idle for an automatic is 750 rpm's the extra 100 rpm's is so it don't die when you put it in gear.. it well drop to 650 when it goes into gear or very close.. don't for get to adjust he air/fuel mixture screws, they are important for idle quality.
Keep us informed.
good luck take care be safe
Tim

 

[Geoff 2]

A mild cam you say.....
I suppose it depends on one's definition of mild....
850 rpm idle seems reasonable, especially if you only have 8-9" of idle vac.

The idle rpm will be what the engine is comfortable with, not some arbitrary number [ like 650 ].

 

[pedal2themetal]

HI,
If you have not adjusted the mixture screws that would cause low vacuum especially if they are out of adjustment.

good luck take care be safe
tim

 

[Geoff 2]

Somebody who put a red cross in post #52....doesn't understand engines.

Something doesn't gel here.....

A mild cam should have about 12-14" of idle vacuum; stock is 16-17". 8-9" of vacuum means a cam that is bigger than mild....or.....it has been installed in a retarded position....or.... has wiped lobes.....or.....vac gauge reading is wrong...or many other possibilities.

 

[kaj750]

Somebody who put a red cross in post #52....doesn't understand engines.

Something doesn't gel here.....

A mild cam should have about 12-14" of idle vacuum; stock is 16-17". 8-9" of vacuum means a cam that is bigger than mild....or.....it has been installed in a retarded position....or.... has wiped lobes.....or.....vac gauge reading is wrong...or many other possibilities.

I have a new vac gauge on the way. It's been a bit over a year since checking, so it's possible I have the number completely wrong.
Gauge should be here on Sat.

Wish me luck!

 

[pedal2themetal]

The idle rpm will be what the engine is comfortable with, not some arbitrary number [ like 650 ].

HI Geoff 2
Just curious how is 650 or even 750 and Arbitrary number when its a factory setting number?

good luck take care be safe
tim

 

[Geoff 2]

Tim.
Ever try to get one of these engines, even a stocker, to idle at 100 rpm? Not going to happen.

That is because the engine is not making enough HP to sustain itself at 100 rpm.

There will be a minimum rpm that [a] produces enough HP to sustain operation & the engine is comfortable with.

Naturally this will be the lowest rpm possible to reduce engine wear & fuel usage.

With a stock engine, the factory will determine this number. You might be able to run a stock engine at a slightly lower rpm than what the factory has nominated. The factory has to err on the side of caution.

Once you go to a cam that has more duration & overlap, a point is reached where the engine is making less HP at lower rpms [ but more HP at higher rpms ]. So the idle rpm has to be increased to make enough HP to sustain operation.

Hope this explains it.

 

[pedal2themetal]

Tim.
Ever try to get one of these engines, even a stocker, to idle at 100 rpm? Not going to happen.

That is because the engine is not making enough HP to sustain itself at 100 rpm.

There will be a minimum rpm that [a] produces enough HP to sustain operation & the engine is comfortable with.

Naturally this will be the lowest rpm possible to reduce engine wear & fuel usage.

With a stock engine, the factory will determine this number. You might be able to run a stock engine at a slightly lower rpm than what the factory has nominated. The factory has to err on the side of caution.

Once you go to a cam that has more duration & overlap, a point is reached where the engine is making less HP at lower rpms [ but more HP at higher rpms ]. So the idle rpm has to be increased to make enough HP to sustain operation.

Hope this explains it.

HI, 100 RPM's LOL LOL who said anything about trying to run it at 100 rpm's..
My 466 with 500 HP TQ, Don't remember much about the cam other it was .516 intake .543 exhaust lift. with a C6 and stock converter .. would idle fine at 750.
Since the original poster didn't know much about carb's I assume he has not set the mixture screws properly and that would cause low vacuum and not wanting to idle at 650 or 750 ...

good luck take care be safe
tim

 

[Geoff 2]

You obviously didn't understand the explanation.......It was actually pretty simple. Try again.