64 Vert - Random Rough Idle When Warm

[smyers1234]

Team - need some help

recently the car has developed a random rough idle after it has warmed up.

does not sound like a vacuum leak or fuel issue, but not dismissing these as options to pursue

The issue is intermittent and almost seems like the car loses spark completely and wants to turn off - spark issue or timing issue? not sure

If I put the car in neutral it wont turn off, but if I place it in drive it will sputter and stall, but only intermittently

Work done thus far:
replaced coil - I'm running Pertronix that is about 3 years old - so I put in a new flamethrower coil - no improvement
replaced the spark plugs - plugs were also about 3 years old - upon inspection the old plugs had normal wear - again no improvement
I am about to put on a new cap & rotor - I will install and re-test and provide an update when completed
I have ordered new Pertronix guts - I will install and re-test and provide an update when completed
I have also ordered new vacuum advance solenoid - I will install and re-test and provide an update when completed

It should be noted that the Pertonix has run fine this past 3 years with the standard resistor wire feed to the coil, but I have ordered a relay and plan on replacing the resistor wire to ensure I get the constant 12v to the coil - I will install and re-test and provide an update when completed

Assuming this does not cure it, seems that perhaps I have a timing issue that perhaps is deeper than my skill set, so I may need to take it to my trusty mechanic, but any advice that can be offered is much appreciated

Spence

[tomo]

It does sound more like a fuel issue than an ignition problem. When the engine is cold, it needs more fuel and idles faster. Once the engine is warm, the choke opens and the idle speed decreases. Excess fuel will cause minor flooding at idle.

To check for a fuel issue, look down the throat of the carburetor with the engine idling. You should not see any fuel dribbling into the carburetor.

I would expect that a failing pertonix would show up as a high speed miss first, but it could show up as an idling problem. Check your spark at a couple of spark plugs with the engine idling. The spark should be blue in color and about 1/2" long.

Check all of the engine compartment vacuum hoses for age related cracks and replace any hoses that are showing signs of cracks.

[action]

Low voltage to the coii for that system is not an issue. It just reduces the voltage that is possible.
But for the application high voltage is not needed. In this aspect Pertonix is so over built for the applicetion.

In a correctly working system the voltage needed is under 10,000. A stock system has the ability to generate 12K to 15K volts
Pertronix (and other systems) can generate 20K to 40K voltage.
This will over come any fouled spark plug or cold weather operation,
A more likely event is the spark finds a ground some where else besides the spark plug.
That can be inside the distributor cap, out a spark plug wire boot or cable

The advantages of Pertronix for this application is extended maintenance and a good spark for longer time

If you suspect ignition, look at spark plug cables, spark plugs, distributor cap and rotor. Some of those you have already done. BTW those 4 items have a service life and should be replaced at a regular interval. The Pertronix, coil and other system pieces should never need replacing.

Vacuum advance sole purpose in the ignition system is to provide better fuel economy. If it fails there is zero impact on the driveability of the engine. Except if the failure is due to a vacuum leak.

To eliminate vacuum leaks as an issue getting a vacuum reading would be necessary. In addition a vacuum reading can tell you a lot about the engine and it's health,

The issue is intermittent. I would tend to believe it is a fuel issue. And the mixture goes too lean. So lean it will not support combustion. The fuel system can get debris, varnish and general dirt.
Make sure filters are clean (air and fuel)
Again get a vacuum reading to understand fuel mixture
If you are comfortable remove the carb bowl cover. (I forget what carb Lincoln used back then) Look for debris in bottom of the bowl.

Action

[Mike]

Carburetor or choke problems can cause issues like that. They all have problems from time to time. Running better in neural then drive is because being in drive even If its not moving puts more load on the engine.

[smyers1234]

Update - the problem still persists -

random thought - can a failing water pump cause the engine to sputter like this? - the engine does sort of feel like it is getting drug down as if its getting stuck - so I was wondering if the bearings are starting to go bad - I plan to remove the belt to inspect the water pump to see if perhaps this is the culprit.

if not, then next steps are:

fuel related - so I plan to have the carb inspected/rebuilt
timing related - going to have the timing set inspected/changed

[frasern]

My first thought would be weak fuel pump, or plugged filter, second would be dirty carb. Also, check the choke stove, you can't get a choke to operate correctly with a plugged one.

Edit, If the water pump is not leaking, the bearing is still good.

[action]

How about a description of what happens, when it happens and the conditions outside when that happens. Without any statement or guess as to cause.
Sputtering with no statements as to when or under what condition is difficult to understand.
The same for, "The engine does sort of feel like it is getting drug down as if its getting stuck"
WHEN?
Accelerating from a stop?
Driving over 45 miles an hour?
For the first 15 minutes of driving at temperatures below 50?
A technican might test drive, We do not have that advantage.
Other diagnostic steps might be necessary. Like a vacuum testing, checking timing or ??? I am not stating that be done NOW but maybe in the future.

So .....
Does the condition happen on a warmed up engine or cold engine
While in park or driving?
If driving how fast?
Accelerating, decelerating or maintaining speed
What are the other side conditions, temperature, sunny temps or cloudy
Since you mentioned water pump, is the vehicle over heating? Or temp gauge higher than what you normally see?

A water pump does not cause a rough idle when warm. A water pump if failing (worn bearings) may cause
Sounds
Leaking water
Higher than normal engine temps IF slower vehicle speeds are the operation
Rough idle, not really.

Then some history on maintenance - When was the last time ..
the air & fuel filter was replaced?
the spark plugs were replaced?
I am going to assume the car sits for long periods. And that would be good to know the driving use the vehicle has seen in last 12 months.

You can have the carb rebuilt and maybe it needs that. But you are guessing. Guessing is OK if you are OK that the results do not change. I can think of at least a half a dozen causes for what I think is happening. You could do all of those and still not fix it. Getting clear on what triggers an intermittent issue isn't easy. Throwing parts at the problem is.

Action

[tomo]

I second Action's statements. You can throw all sorts of parts at the car and the result could vary from making the car useless to fixing the problem without knowing what fixed it. The knowing what fixed it is important in case it fails again. Do the checks that he mentions and the following ones if it is not fixed. Intermittent symptoms are hard to diagnose, so you have to persevere an keep trying to find the source of the failure.

Check the carburetor by looking down the throat of it while the engine is idling. There should be no sign of fuel dribbling into the venturi. Check all vacuum hoses for small crack or signs of hardening, replace the ones that look old.

[LC67Vert]

My '67 would start fine when cold and then run poorly once warned up. I decided to rebuild the carb and discovered one float had a pin hole that would allow fuel to get in it which would cause the float to stick open and flood the carb with too much fuel causing a rough running condition. If your carb has not been rebuilt in a long time it may the reason for your problems.

[smyers1234]

let me attempt to better explain the situation

Issue/Condition - Rough Idle at full operating temp and when car is in drive at stoplight
The car is fine for first 30 minutes of driving, but once it gets to operating temp it begins to have this rough idle condition
This rough idle condition occurs when I am at a stoplight and have the car in drive
It runs fine, but then is falters/sputters for a brief second and then goes back to running fine
the car will do this a number of times while at the stoplight

When I take off the car runs fine, however as I continue to drive the car, the rough idle condition feels like it gets worse and even sputters a bit as I take off from the stoplight, and really sputters if the car is under load, which occurred today as I was going up a slight hill

things I have done, that have not corrected the issue:
changed spark plugs
changed spark plug wires
changed cap & rotor
changed pertonix coil and pertonix components inside the distributer
changed fuel filter
had the car re-tuned for best mixture and changed suspect vacuum hoses
The fuel pump is less than 6 months old

I attempted to try to capture the car with video, but it is tough to tell what is going on so I have not posted it here

I have been monitoring the condition with my voltmeter since this seems to be the only way to visualize what is going on
at start-up with car in neutral the voltage is around 14.5v to 14.7v and bounces around a bit
once I put the car in drive with wheels chocked the voltage drops to 14v (which makes sense since the car is under load)
as the car continues to warm up I notice that the voltage averages around 13.6v to 13.8v
then as the car sputters it drops down to 13.2v to 13.4v and then goes back up to 13.6v to 13.8v
now just because the voltage is moving around I don't necessary think there is a correlation, but trying to monitor what I can to find a connection

Driving and Maintenance history:
I have had this car for 5 years and drove it almost every day for the first 4 years
When I first got the car, I did a bunch of things to improve drivability (pertonix, wrapped the fuel lines with insulation, new fuel pump, new fan clutch, secondary fan, all new wires, positive power cable, negative cable + verifying that it had good connection to chassis, new voltage regulator, new alternator (not a 1 wire), battery cut-off switch, re-built radiator, new tires, new brake lines, new convertible top lines, etc) but the car always has run fine

For this past year I have only driven it about 1 or 2 times a month - mostly on weekends and this issue began in February of 2021

as spring has come I find myself driving the car more and more and plan to go back to driving it daily back to work once I get this rough idle fixed

appreciate the support and assistance!

my next step once I get more advice from you guys is to have the carb re-built - my local mechanic is familiar with these cars and carb re-builds

until next time my firends!

[TonyC]

No input to offer, as I have my own engine problems...but I'll be watching the progress of this thread, see if someone suggests something I haven't thought of. OP's problems, efforts, and even the time the problems began are very similar to my own.

---Tony

[action]

Sounds like the carb is set up too lean. Not by a lot. (Or there is some dirt blocking a passage)
The idle mixtur circuit is in play from idle to about 30 or 35 in high gear.

That issue is masked when the engine is cold because the choke is enriching the fuel mixture. Once the choke fully opens the condition can be felt.

Similar to that would be a vacuum leak. Not a big one. One that does the same thing as a lean idle mixture.
Again once the choke masks that condition.

Getting a vacuum reading would be the next step.

Action

[smyers1234]

Well saga continues

update:
Replaced Carb with new Stock carb from Summit Racing - Edelbrock, part # EDL-1406

that part is running great, plus found out original carb did not have the choke set up properly, so now that works much better (has not been a problem since I live in California)

But, the same problem persists

Problem - engine runs sluggish, and feels like it wants to shut off for a brief second and then continues along - its like it falters a bit and then runs just find.
Also after I have been driving for a bit, I go to jump on it and it feels sluggish and also a few times, the engine almost died while trying to accelerate, but then it quickly recovered.

I put high octane fuel + some marvel mystery oil in the oil and the gas, and drove it around town like a maniac, trying to blow the cobwebs out of the engine, but still same issue.

Now - what next? - wondering if I have either sticking valve or bad timing chain issue

any thoughts?

[action]

Check base ignition timing with vacuum advance disconnected.

Warm up engine and post engine vacuum readings

Action

[smyers1234]

Team - update - car working again!

turns out the mechanical weights inside my distributor were sticking causing the car to not advance correctly and run roughly.

they have been lubricated, but I would like to replace my distributor

can someone please provide a place to order and the correct part numbers.

thanks!