Sudden rough running, out of ideas

[alexiskai]

Wanted to circle back to this since I finally had time to make some changes:

• Replaced intake/exhaust manifold with good used manifold
• Had manifold surfaced
• Used a Dremel to grind smooth everything I could reach in the intake/exhaust system
• New copper gaskets for the manifold and carb with copper spray-gasket
• Disassembled the (practically-new) Bert's carb and checked all jets for debris
• Sealed the manifold/muffler joint
• Re-did the timing (was off about 10°)
• Fiddled extensively with the GAV, idle screw, and spark advance

After all that I think I was able to get the idle down a little bit. Not to where it was when I got this car 2 years ago, though.

Also I discovered that the rebuilt Bert's carb had been sent with a filter screen that had stripped threads. First time I opened the gas cut-off, a steady stream of gas came out the front of the carb where the screen inserts. I rigged up a temporary plug by putting a nut halfway up a 1/2x20 bolt, threading the bolt a few turns into the carb, and then tightening down the nut to seal it. Still leaks a bit but it'll work until the new part arrives.

Haven't had time to drive it yet to see if it still stalls on stop. If it does then I'll really be out of ideas.

[30 Closed Cab PU]

Not sure at this point what you know, or what has been troubleshot after all of your efforts above. Seems at this point we are unsure if it is a carb/fuel mixture issue, or if an ignition issue. You may want to run ignition and plug reads again. Do not mean to insult you, just reviewing what I think I know, others can chime in and correct me where needed.
Here is a site with lots of Carb info that is supported by Berts. More info than you probably want, but perhaps it will give you additional ideas.


https://www.modela.org/


Not sure where you stand at this point since so much has been attempted. Do another plug read to base line the carb.


Perhaps resort to a timing light to see were your advance at idle is at, and if it is stable or varying. You could also try an ignition tester to see the quality of your spark at each plug, there are a few different types, this is my preference.
https://www.mikes-afordable.com/product/T12117.html


On an A plug reads are done from running at med/high speeds and should be tan on the center porcelain. Black but not sooty is ok on the rest of the plug. Clean up plugs, run at higher speeds (country driving for awhile), turn off ignition and chop the throttle, coast to side of road or parking area, read plugs. At idle /lower speeds it is not uncommon for the porcelain to be black, but not sooty.


My understanding of Carbs.
At idle rpms (650 rpm and less) the carb idle mixture screw controls mixture, GAV does not affect the mixture.
At fast idle (above 650 rpms) to med speeds (revs) the GAV affects mixture and the idle mixture screw mostly does not affect the mixture.
The higher the motor speed (revs) the GAV has less affect on the mixture as the Jets take over most control of the mixture. The GAV still has some effect, will run very lean if GAV is completely closed. If running closed you may have poor running at lower speeds , and perhaps a slight pop/backfire when shifting or letting your foot completely off the gas, and will not fast idle. Typically adjustment of GAV a little richer solves this.
If plugs are sooty at higher speeds could try a hotter plug, or the issue is with the jets or a vacuum leak.

[30 Closed Cab PU]

If unresolved you may be at a point where you need want to remove the valve access cover and check to see if the valves are seating properly on cylinder 2. You still have weak compression of 50lbs compared to 60-65lbs on the others. Maybe you will get lucky and have a sticky valve, or a piece of carbon under one of the valves and it can be resolved without removing the head.

[ryanheacox]

Have you put a vacuum gauge on it? That is, if you have a port on the intake manifold.

That low idle might come back if you push the throttle closed at the carb. My throttle plate was ever so slightly out of alignment and wouldn't close completely resulting in a high idle. Adjusting the throttle plate dropped my idle considerably.

Most common fix for stalling on a fast stop is to adjust the float level.

[alexiskai]

Originally Posted by ryanheacox

Have you put a vacuum gauge on it? That is, if you have a port on the intake manifold.

That low idle might come back if you push the throttle closed at the carb. My throttle plate was ever so slightly out of alignment and wouldn't close completely resulting in a high idle. Adjusting the throttle plate dropped my idle considerably.

Most common fix for stalling on a fast stop is to adjust the float level.

• I do have a vacuum port. What would I be looking for on the gauge reading?
• I'll try that throttle plate idea
• Gonna hold off on the float level adjustment for now but I might end up there.

Originally Posted by 30 Closed Cab PU

If unresolved you may be at a point where you need want to remove the valve access cover and check to see if the valves are seating properly on cylinder 2.

Assuming I take the valve cover off, what am I looking for?

Originally Posted by 30 Closed Cab PU

You could also try an ignition tester to see the quality of your spark at each plug, there are a few different types, this is my preference.
https://www.mikes-afordable.com/product/T12117.html

I actually have this tool but I've only used it to check the main spark to the distributor cap. Can it be used per plug?

Originally Posted by 30 Closed Cab PU

My understanding of Carbs.
At idle rpms (650 rpm and less) the carb idle mixture screw controls mixture, GAV does not affect the mixture.
At fast idle (above 650 rpms) to med speeds (revs) the GAV affects mixture and the idle mixture screw mostly does not affect the mixture.

I think I'm still in a fast idle, because what I noticed when adjusting the idle mixture screw was:

• Opening the screw, make several turns, eventually engine stalls
• Closing the screw, close it all the way down, I can hear a difference in the whistling of the air going into the carb but the idle is unaffected; cannot get the engine to stall by closing the idle screw.

... whereas when I was at idle I was able to adjust the RPM by adjusting the GAV. It seemed happy at about 1/4-turn open.

Thanks everyone for the continued feedback, I still hope to get this resolved.

[30 Closed Cab PU]

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Vacuum gauge info


http://www.fordgarage.com/pages/vacuumtune.htm


Here is the string it is in.
https://www.fordbarn.com/forum/showt...t=vacuum+guage


More info
https://www.fordbarn.com/forum/showt...t=vacuum+guage

[alexiskai]

Originally Posted by 30 Closed Cab PU

Vacuum gauge info


http://www.fordgarage.com/pages/vacuumtune.htm

This is awesome. I love "inject penetrating oil into manifold," that sounds like fun. Definitely will get one of these.

Edit: Just bought one off eBay, will have a report in a week or so.

[ryanheacox]

Some good links there. If you don't have a vac gauge, horrible freight sells one for ~$15 and it works decently well. It might not be the best way to diagnose a problem but it should give you some good info to work with.



Also, note that last sentence on the fordgarage link. If you see a reading like that, I would definitely be looking at the throttle plate alignment.


Definitely hold of on adjusting the float until you know how the car performs. No need to pull the carb back apart unless you know you have to.

[ryanheacox]

Originally Posted by alexiskai

This is awesome. I love "inject penetrating oil into manifold," that sounds like fun. Definitely will get one of these.

Right, that was another question. Do you use anything in your gas? MMO or 2-stroke oil? That low compression could be a sluggish valve. Not sure if someone said that yet or not.

[alexiskai]

I do not use MMO in the gas, but I have some on hand and, based on that other MMO thread, seems like it's worth a try.

Just bought this guy for $18, looking forward to taking some readings and reporting back.

[30 Closed Cab PU]

Originally Posted by alexiskai

• i do have a vacuum port. What would i be looking for on the gauge reading? info sent above
• i'll try that throttle plate idea
• gonna hold off on the float level adjustment for now but i might end up there.

assuming i take the valve cover off, what am i looking for? - with ignition and gas off, crank the engine and ensure the # 2 valves are completely opening/closing. Another thing you can do is to use an inexpensive borescope through the spark plug hole to inspect the valves when they are closed, for seating.


also you could in a dark shop (lights off) shine a flashlight through the spark plug hole and see if any light is leaking through into the valve chamber. - ignore this, had a brain fart.


if not sticky valves, and suspect carbon, have heard that using water/misting bottle through the carb intake at fast idle can help. Have not tried this myself.


for sticky valves, mmo (marvel mystery oil) in the gas helps, some spray it directly in the teh vacuum port on teh intake manifold while car i is running. You may be able to free a sticky valve by manually moving it up and down.


with ethanol gas and the age of these cars 4 ozs of mmo per tankful helps prevent sticky valves, and also helps with preventing carb float valve seating issues.




i actually have this tool but i've only used it to check the main spark to the distributor cap. Can it be used per plug? - as is no, i made an adapter to do this. But if you have it plugged into teh distributor, all flashes should be equal intensity spark. If you see occasionally weak sparks or even a missing spark - problem.



i think i'm still in a fast idle, because what i noticed when adjusting the idle mixture screw was:

• opening the screw, make several turns, eventually engine stalls
• closing the screw, close it all the way down, i can hear a difference in the whistling of the air going into the carb but the idle is unaffected; cannot get the engine to stall by closing the idle screw.

... Whereas when i was at idle i was able to adjust the rpm by adjusting the gav. It seemed happy at about 1/4-turn open. - you are not idling low enough. At low idle gav does not affect the idle from almost completely closed to 1 -1/2 turns on teh gav.


idle mixture screw is only adjusted correctly at low idle.


when you got your bert's carb, they ship a procedure. Usually it is not needed. Here is a link to the procedure for adjusting.
https://www.modela.org/idle_adjustment.html


if you can not follow this, then you have another issue, perhaps the valves not seating properly to allow you to get to low idle?

thanks everyone for the continued feedback, i still hope to get this resolved.

111111111111

[30 Closed Cab PU]

Originally Posted by ryanheacox

Some good links there. If you don't have a vac gauge, horrible freight sells one for ~$15 and it works decently well. It might not be the best way to diagnose a problem but it should give you some good info to work with.



Also, note that last sentence on the fordgarage link. If you see a reading like that, I would definitely be looking at the throttle plate alignment.


Definitely hold of on adjusting the float until you know how the car performs. No need to pull the carb back apart unless you know you have to.

Almost missed this, pretty funny, you made my day Ryan

[30 Closed Cab PU]

Edited my post #91 - had a brain fart.

[alexiskai]

OK, thanks, so my to-do list is:

• 4 oz MMO in the gas
• Install vacuum gauge, see what's up
• Check for equal-intensity spark on all 4 plugs
• Run that carb calibrating procedure

Gonna hold off on removing the valve cover for the moment because it's a pain and I'll probably need to replace the gasket. If it is valves (based on vacuum reading), I'll see if I can free them up with MMO or penetrating oil.

[ryanheacox]

Sounds like a good plan.

[barnstuf]

Five pages of information and no one has suggested that an easy way to find ignition system short circuits is to run the engine at night in total darkness. No guaranty of course but sometimes the problem is quickly solved if ignition related.

[alexiskai]

Originally Posted by barnstuf

Five pages of information and no one has suggested that an easy way to find ignition system short circuits is to run the engine at night in total darkness. No guaranty of course but sometimes the problem is quickly solved if ignition related.

Is there reason to think that the current stage of the problem (fast idle) may be related to a short circuit?

[30 Closed Cab PU]

Is the motor running rough, not even firing at idle?


Sometimes sneak paths are resistive, causing marginal/poor spark instead of a direct short. An example is a bad distributor body where the internal electrical path from the dist. internal contact to where the spark plug wire is connected has opened, or the body has developed a resistive path to ground. This is why it is best to clean off the distributor parts to prevent dirt/lube/etc from creating a sneak path to ground. .


Running at night sometimes allows you to see a sneak path .


I've seen mechanics in the past use a water misting bottle while the motor is running to trouble shoot this, and to trouble shoot bad (too high resistance) plug wires in modern cars.

[alexiskai]

Although the title of the thread is "rough running," somewhere along the five pages of posts I got that fixed. However the fast idle remains.

[30 Closed Cab PU]

Originally Posted by alexiskai

Although the title of the thread is "rough running," somewhere along the five pages of posts I got that fixed. However the fast idle remains.

Thanks for clarifying.


So is a case it is stalling, or a case of not being adjustable enough at the carb and or steering column lever, or running erratically when running at low rpms and then stalling?