Slowly....dying...

[kaj750]

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:

 

[Don Frelier]

That's an ammeter and your description of operation is totally normal.
The speedometer issue is unrelated.

Ignition timing and idle mixture could need adjustment. But I would start by turning in the idle speed screw a bit.

 

[R413]

Better fix that speedo before it breaks, and it will soon.

remove cable from speedo, pullout center with needle nose, clean it with brake clean and a lint free towel, lube it, reinstall in housing, put a small amount of lube on back of speedo end, put cable Back on.

do not use white lithium in a spray can, it hardens after some time.

 

[kaj750]

That's an ammeter and your description of operation is totally normal.
The speedometer issue is unrelated.

Ignition timing and idle mixture could need adjustment. But I would start by turning in the idle speed screw a bit.

Knowing it's not a voltage gauge makes me feel a bit better that it's not reading higher. I've never had a gauge in a car reading amps, so I have no idea what to expect from it.

It already idles at 850 when in park. Not sure I want it higher. Car ran just fine a month ago. It is a lot cooler now, though.
I'd hate to have a 1000RPM idle, just to keep it from dying at a stop light.
At one point, last winter, the car got so bad at finally died on me. Ended up having it towed home. Put the battery on a tender, drove fine after that. Ended up swapping carburetors and doing some other work during the winter. When I went to drive the car during warmer months with the new carburetor and battery, it was awesome.
Now that it's cold outside, here we go, again lol

 

[LowBikeMike]

A proper Ammeter reading would be with needle centered at 0. It will show a little charge after starting, then should settle to 0. What is the condition of your battery?. Depending upon ignition type a weak battery/charging system could cause your issue. What is your voltage at the battery with engine idling?

 

[Geoff 2]

What carb?

 

[Demonic]

Have you checked your plugs after the carb change? Sounds like the warm idle needs adjustment or it's loading up.

 

[tonysrt]

Another engine running problem could be a vacuum leak or a bad pcv.

 

[Car #4]

As for your speedometer problem, is it the original speedometer or aftermarket? Either way it sounds like it needs to be rebuilt if doing the lube treatment on the cable doesn’t work. Send it to Redline Gauges in California. I’ve had them do two in the past year. They aren’t cheap but they are very good at what they do. I’m not so sure I’d have an aftermarket speedometer rebuilt though, I don’t have much faith in them based on experience. Better to hunt down a used original.

 

[kaj750]

A proper Ammeter reading would be with needle centered at 0. It will show a little charge after starting, then should settle to 0. What is the condition of your battery?. Depending upon ignition type a weak battery/charging system could cause your issue. What is your voltage at the battery with engine idling?

Battery is new, but still.... You know how that can go

I'll have to go back, today, with my volt meter. I can't remember the exact number, off the top of me head.
I'll check it when I get home and report back.

 

[kaj750]

What carb?

750 Eddy. Solved ALL of my problems until just recently.

Another engine running problem could be a vacuum leak or a bad pcv.

Vacuum was spot on before this, I haven't checked since. Will do.

As for your speedometer problem, is it the original speedometer or aftermarket? Either way it sounds like it needs to be rebuilt if doing the lube treatment on the cable doesn’t work. Send it to Redline Gauges in California. I’ve had them do two in the past year. They aren’t cheap but they are very good at what they do. I’m not so sure I’d have an aftermarket speedometer rebuilt though, I don’t have much faith in them based on experience. Better to hunt down a used original.

OEM. I'm not into aftermarket stuff on a classic car. I'm stubborn.

 

[Sixpactogo]

No one mentioned it but concerning your first issue with engine wanting to die, I would suspect fuel starvation. Possibly could be fuel filter or sock in fuel tank clogged up. I would start by replacing the fuel filter and cutting up the old one to see how much gunk is in it. If a lot, I would be looking at cleaning the fuel tank and put a new sock on it. There are other reasons but it is a place to start.
Speedo issue could be cable related or the speedo head itself dried out and needing rebuild.
Amp meter readings seem normal to me. If it was showing a minus it would be cause for concern.

 

[Don Frelier]

No one mentioned it but concerning your first issue with engine wanting to die, I would suspect fuel starvation. Possibly could be fuel filter or sock in fuel tank clogged up. I would start by replacing the fuel filter and cutting up the old one to see how much gunk is in it. If a lot, I would be looking at cleaning the fuel tank and put a new sock on it. There are other reasons but it is a place to start.
Speedo issue could be cable related or the speedo head itself dried out and needing rebuild.
Amp meter readings seem normal to me. If it was showing a minus it would be cause for concern.

Good suggestion on the starvation possibility. Pretty easy to take the top off of an Edelbrock/Carter and visually inspect.
You can also disassemble and blow everything out without changing anything if your kind of careful.

 

[mattsmopars]

As far as the running issue, I had a similar issue where my car would run while cool, but with engine temperature and time it would want to stop idling and die unless you actually gave it fuel. I could cover the carb top with my hands and it would idle up. So with that information I could tell it was to lean at idle. so I added a 1/2 to the idle mixture screws and that seems to have cured that issue.

 

[kaj750]

No one mentioned it but concerning your first issue with engine wanting to die, I would suspect fuel starvation. Possibly could be fuel filter or sock in fuel tank clogged up. I would start by replacing the fuel filter and cutting up the old one to see how much gunk is in it. If a lot, I would be looking at cleaning the fuel tank and put a new sock on it. There are other reasons but it is a place to start.
Speedo issue could be cable related or the speedo head itself dried out and needing rebuild.
Amp meter readings seem normal to me. If it was showing a minus it would be cause for concern.

Fuel filter is clean. Fuel coming up to the carburetor is clean. Fork pressure is 6-7psi. Car runs amazing under throttle.
The car just seems to lose electrical power the longer I drive it.
I assume the cluster and headlights are dimming because the idle is dropping. Maybe it's the other way around.

 

[68-500]

I believe it maybe bordering on running to lean. In the warmer summer months not as much gas is required to to mix with the warmer, thinner air. In the cooler winter the same cubic foot of air requires more gas to maintain the same a/f ratio, due to the oxygen molecules being more densely packed. Adjust idle screws. Or raise float level.

 

[kaj750]

I believe it maybe bordering on running to lean. In the warmer summer months not as much gas is required to to mix with the warmer, thinner air. In the cooler winter the same cubic foot of air requires more gas to maintain the same a/f ratio, due to the oxygen molecules being more densely packed. Adjust idle screws. Or raise float level.

Car now idles at 1000 RPM and 800ish in Drive, until I drive for a bit, then it's 1000 idle and 500ish in gear.
Usually these carbs don't need so much work.

 

[Sixpactogo]

OK.....Now you got me thinking you need to adjust the idle circuit on the carb. It is on fast idle cold and drops off when it gets warmed up. Just turn that screw up a turn, that will more than likely fix it for you.

 

[kaj750]

OK.....Now you got me thinking you need to adjust the idle circuit on the carb. It is on fast idle cold and drops off when it gets warmed up. Just turn that screw up a turn, that will more than likely fix it for you.

Will try that asap.
Wish me luck

 

[Geoff 2]

You may have leaking n/seats in the carb. While cruising that extra fuel gets used up & you do not notice any problems. At idle, where very little fuel is reqd, it runs rich, idle rpm drops, worse the hotter the engine gets. Remove carb top & check n/seats & for fuel logged floats.