/6 Idling Problems

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SmokeJumper69

SmokeJumper69

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I have a '66 Dart with the 225 Slant 6. I have a Holley 1920 carb. and I'm running points. It's got the automatic tranny. I have a problem I'm not 100% sure on the cause. I start her up and let her warm up for about 5 min before driving. Put her in drive and start going. She runs fine during the first couple minutes of driving. Once I get going on the highway and have to stop at a red light, or NYC traffic, she runs REALLY ROUGH when the tranny is engaged and my foot is off the gas. If I don't rev her up or throw the tranny in neutral she'll ping real bad and shut down. I just picked up a carburetor rebuild kit and I just installed new cap, rotor, wires and plugs. I was hoping someone out there could give me anything else to look at after I rebuild the carb.
 
How long on the highway? Have you checked for vacuum leaks? Does the choke open up? Does the choke pull of work OK? Did you check the piont by dwell or gap?
Lynn
 
From my experience... New points and stuff for a worn out distributer was a waste of coin. After adjusting valves, rebuilding carb and everything else I could think of, the idle still changed on an almost hourly basis.
When I finally bought a reman'd distributer it came with new parts. It was like dipping that old car in the fountain of youth too.
This was back when autozone was autoshack. i made them get me 3 different distributers before I got one that had nearly zero play in the shaft / point gap.
 
Smokejumper69,

Shoot me an email or PM with your address. I have a NOS rebuilt 1968 225 points distributor that I used in the tests 2875366. I also have a used vacuum can 2875794 (11 on arm) that I just checked with my Mighty Vac and it seems just fine.

I am done with the distributor gear tests and would be glad to see them in use. Hope they will help. Jersey is Samantha's old stomping grounds.
 
The vacuum hoses are all rock hard. My plan is to rebuild the carburator and install new points and condenser, I might just get a new distributor and vacuum can from Kevin, THANKS! I'm going to replace all my vacuum lines as well and re-set the timing. Judging by your comments I think it's the right move. But this morning something else happened. My idiot light for oil went on whenever I let it sit at idle in gear or not. I checked the oil level and it's good. Dirty, but good. Do you guys think by doing all this that it will solve the oil light problem too or should I change out my oil pump too?
 
it takes only 9 pound average to turn the warning lamp off. If the pickup screen is clogged the filter needs changed and the idle is very low, the lamp will come on. Lets get it running right, change the oil and filter and see what happens. If that light still comes on idling hot in gear, drop the pan and clean the pickup. New oil pump or not is your decision.
 
I had a 69 Dart Slant Six for 19 years. For 18 years it always idled rough and often died if I didn't keep tapping it at stop lights. This was thru several valve jobs, 1 engine rebuild, a new long block, at least 2 carbs (Holley 1920), and Crane Cams XR700 electronic ignition. I suspected poor venting in the tank or boiling in the supply lines. After it still idle bad after the long block, I tried a 3rd (or 4th) carb. It then idled extremely smooth and rev'ed on command. No more stumbling or delays. This suggests there are a lot of bad rebuilt 1920's, or maybe they have a design defect. The good carb had a hole drilled from outside into the barrel. I thought a mistake, but maybe that was the solution.

Another subtle thing is distributor phasing, meaning insure the rotor aligns with the tower when it sparks. Usually designed-in with points, but some people don't think of phasing when they add electronic pickups. The way to check is drill a hole in a spare cap at the #1 and look at the rotor with a timing light. It should align, with slight lead with engine speed and vacuum. If in between 2 towers, it can spark 2 cylinders at once.
 
That is really interesting. Do you think you could indicate where the hole was on this exploded diagram?

http://www.oldcarmanualproject.com/manuals/Carbs/Holley/TypicalViews/pages/1920.html

BillGrissom said:
I had a 69 Dart Slant Six for 19 years. For 18 years it always idled rough and often died if I didn't keep tapping it at stop lights. This was thru several valve jobs, 1 engine rebuild, a new long block, at least 2 carbs (Holley 1920), and Crane Cams XR700 electronic ignition. I suspected poor venting in the tank or boiling in the supply lines. After it still idle bad after the long block, I tried a 3rd (or 4th) carb. It then idled extremely smooth and rev'ed on command. No more stumbling or delays. This suggests there are a lot of bad rebuilt 1920's, or maybe they have a design defect. The good carb had a hole drilled from outside into the barrel. I thought a mistake, but maybe that was the solution.

Another subtle thing is distributor phasing, meaning insure the rotor aligns with the tower when it sparks. Usually designed-in with points, but some people don't think of phasing when they add electronic pickups. The way to check is drill a hole in a spare cap at the #1 and look at the rotor with a timing light. It should align, with slight lead with engine speed and vacuum. If in between 2 towers, it can spark 2 cylinders at once.
Click to expand...
 
Kevin,

My '69 Dart was stolen in 1994, so from memory. I recall the hole was drilled in the smooth part of the throat, opposite the bowl, about halfway vertically as in diagram. About the diameter of a Q-tip stem (1/16"D?), since I put one the hole to filter (hollow plastic stem). At first I thought to plug the hole since I thought maybe a CNC machine went crazy, but it seemed to run better with it open. I got the good carb thru auto parts in Boron, CA.

The rough idle seemed a lean problem, but adjusting the needles and even drilling the jets didn't work. You could optimize a little with the needles, but never get it right. It would idle OK in neutral, but in drive it slowed way down and stumbled, sometimes dying when you tried to accelerate. My wife hated driving the car. I have a Holley Projection on a Newport and it acts the same if you turn the idle too lean.

I suspect a mixture distribution problem. Slants are bad, with different sized runners. The fuel droplets don't follow the air around turns, especially at idle where the fuel dribbles in from the idle circuit. The hole was above the throttle plate and idle fuel enters below the throttle, so not sure how the hole helped, especially since opposite where fuel enters.

There are other carbs for Slant Six's, like a Carter 1 barrel. You might ask others what has worked best. If I still had my six, I might have tried a Super Six manifold w/ 2 barrel or even an Offenhauser 4 barrel with a 370 cfm carb. In theory, a spread-bore carb (small primary bores) gives better low speed operation than a 2 barrel. Even better, you could mount a small throttle body and control with a Projection or Megasquirt controller. Multi-port injection enforces fuel distribution, but that requires custom machining and welding for a Slant.

BTW, the City of Atlanta was helpful on my stolen car. After 4 yrs, they sent a postcard requiring a reply or they would "unfound the crime". The mayor wanted to improve crime statistics. After 6 yrs, the Marietta Police recovered my license tag on a stolen Jetta, but not the car. Some suggested I cruise the projects looking for it, but I always thought it was rednecks.

Holley 1920.jpg
 
Hi Bill,

I was looking at the Holley carb adjustment spec chart (in my Motors manual it goes from 1965 to 1971). The bowl vent spec for the 1969 Holley 1920 is 3/32" clearance. In 1971 it drops down to 1/32" clearance. I am wondering if your feeling that it had something to do with venting was right on the money. It might be the last carb was set to a slightly greater clearance or the vent worked differently on it. It sounds like the carb with the hole drilled in it was set up for some type of smog fitting, otherwise unfiltered air would be a no-no. The bowl vent works when the throttle plate is closed during idling. If the clearance was too small it would tend to lean out the mixture (my understanding -- I am not an expert in this).

I know when I bought a rebuilt carb for my Grand Wagoneer they assured me it was correct for the application but it turned out to be missing the altitude adjustment parts found on the Jeep version.


Edit: Maybe we will read about your Dart being recovered someday completely restored. Maybe even with a built hemi stuffed into it. ;-)



BillGrissom said:
Kevin,

My '69 Dart was stolen in 1994, so from memory. I recall the hole was drilled in the smooth part of the throat, opposite the bowl, about halfway vertically as in diagram. About the diameter of a Q-tip stem (1/16"D?), since I put one the hole to filter (hollow plastic stem). At first I thought to plug the hole since I thought maybe a CNC machine went crazy, but it seemed to run better with it open. I got the good carb thru auto parts in Boron, CA.

The rough idle seemed a lean problem, but adjusting the needles and even drilling the jets didn't work. You could optimize a little with the needles, but never get it right. It would idle OK in neutral, but in drive it slowed way down and stumbled, sometimes dying when you tried to accelerate. My wife hated driving the car. I have a Holley Projection on a Newport and it acts the same if you turn the idle too lean.

I suspect a mixture distribution problem. Slants are bad, with different sized runners. The fuel droplets don't follow the air around turns, especially at idle where the fuel dribbles in from the idle circuit. The hole was above the throttle plate and idle fuel enters below the throttle, so not sure how the hole helped, especially since opposite where fuel enters.

There are other carbs for Slant Six's, like a Carter 1 barrel. You might ask others what has worked best. If I still had my six, I might have tried a Super Six manifold w/ 2 barrel or even an Offenhauser 4 barrel with a 370 cfm carb. In theory, a spread-bore carb (small primary bores) gives better low speed operation than a 2 barrel. Even better, you could mount a small throttle body and control with a Projection or Megasquirt controller. Multi-port injection enforces fuel distribution, but that requires custom machining and welding for a Slant.

BTW, the City of Atlanta was helpful on my stolen car. After 4 yrs, they sent a postcard requiring a reply or they would "unfound the crime". The mayor wanted to improve crime statistics. After 6 yrs, the Marietta Police recovered my license tag on a stolen Jetta, but not the car. Some suggested I cruise the projects looking for it, but I always thought it was rednecks.
Click to expand...
 
Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download. Tune-up parts and technique suggestions in this thread. Rough idle can also be caused by improper valve adjustment. You may also want to do the Fuel line mod. The hole through the carburetor bore wall is found on some Holley 1920s, Carter BBSs and BBDs, Stromburg Ws and WWs, and other carb designs—not on others. It's not a vent, it influences the calibration of the vacuum-operated transitions (power valve, distributor vacuum advance). See this thread for details.
 
http://u225.torque.net/cars/SL6/docs/Holley_1920_Manual.pdf

Man, isn't that aggravating when you go to a rebuild or service diagram and they show you a later model of the carb. Grrrr. *

Lots of good info in those threads about deposits that build up in difficult to access passages. You might try an ultrasonic cleaner along with the suggestions in the threads.

I used to use piping hot beakers of carbon tet and methylene chloride in the sonicators to clean up nasty dirty greasy stuff on small metal pieces -- alas illegal stuff now (be very careful what solvents you choose as some will aggressively attack/destroy plastics).

* Aside: So, I have carefully collected a number of internet recommended manuals and pictures for cleaning my Mercedes transmission valve body assembly. I open it up and parts, springs, ball bearings, little plastic bits, etc. start dropping-out/launching onto the work table. I then see that the pics don't match the particular valve body version I have have. Nice.
 
My 6 banger was running rough until I found the leaky diaphram for the vacumn advance which was essentially giving me no advance plus a vacumn leak. I replaced it with another one I had lying around and she idled much better.
 
Kevin Johnson said:
I used to use piping hot beakers of carbon tet and methylene chloride
Click to expand...

That's quite explanatory; both of those solvents are severely neurotoxic, and the effect is cumulative.

It always bears repeating: chemicals strong enough to clean a carburetor are by necessity extremely aggressive. They will dissolve the gluelike varnishes and gums and other kinds of gunk that you want gone, then they move right on to strip the anticorrosion coating off carburetor castings in a fairly big hurry (20 minutes to 2 hours or so, depending on strength/freshness and temperature of the cleaner).

It will also dissolve your hands, eyes, sinuses, etc. No matter how you are exposed to it -- by inhalation, by skin contact, etc. -- it will also work at dissolving your lungs, and it will dissolve the fatty matter that makes up your brain. Over time, this causes cognitive and behavioural problems similar to those seen in longtime body-and-paint men. At risk of sounding like I'm preaching, if you use this stuff, use it as intended (dipping, not splashing/pumping/spraying) and be about 3x as careful as you think you should be. I'm talking extremely good ventilation, completely shielded skin and eyes, etc. Methylene chloride by itself is grievously injurious to life. It is seriously toxic, causes cancer, and is readily absorbed through skin (liquid) and via mucus membranes and lungs (vapour). Add in the other strong chemicals found in these dip-type cleaners (MEK, toluene, acetone...) and you really do have a toxic waste dump in a 5-gallon can. These products, when used safely and carefully and disposed of properly (that can be a real trick!) can be useful for seriously filthy parts, but you have to handle them with great respect and caution.

be very careful what solvents you choose as some will aggressively attack/destroy plastics
Click to expand...

If there are any nonmetallic components left on the carburetor you're about to dip into carb cleaner, you're doing it wrong. And a further comment on the anticorrosion coatings mentioned above: carburetor castings stripped of their anticorrosion coatings are quite pretty when they come out of the dip, but once placed into service, they corrode very rapidly. The potmetal (zinc die cast) of which most carb castings are made forms a dense, powdery corrosion that is all but impossible to remove successfully, and even if you could, the "eaten" metal no longer conforms to the precisely-machined and -drilled dimensions; passages are either clogged solid or grossly oversized, etc. This is one of the main causes of permanent death in the Holley 1920 carburetor -- irreversable buildup of crud and destruction of critical dimensions in the main metering block. It is also one of the reasons why "remanufactured" carburetors tend to be such junk; they are abusively "cleaned" with abrasive means (blasting -- it might not be sand, it might be soda or some other material, but it strips the coating nevertheless, and the coating is usually not reapplied).
 
My gosh, thank heavens for exhaust hoods.

Cresylic acid used to be a common component in carb cleaners as well.

Thanks for the refresher on chemical dangers. I had almost forgotten them from when I used to sell specialty and industrial chemicals to car products formulators.

One nasty but fairly common one that is far more dangerous than carbon tet or methylene chloride is HF, or hydroflouric acid. This is sometimes found in automotive aluminum brightners The flouride ions migrate rapidly through unprotected skin and can cause rapid death. Users are cautioned to have topical antidotes immediately available.

http://emedicine.medscape.com/article/773304-overview
 
Ok, so after reading all those threads and links on carbs over on dot org (thanks, Dan), I see that the correct info on the vent clearance for what year carb you have is not given. Is this possibly why there have been so many idling problems for the Holley 1920? That is way too scary to contemplate.

Anyways, you have to learn to check things out for yourself using period primary source references and don't believe everything you read on the internet.
 
Kevin Johnson said:
Ok, so after reading all those threads and links on carbs over on dot org (thanks, Dan), I see that the correct info on the vent clearance for what year carb you have is not given.
Click to expand...

It's not a terribly crucial adjustment. As long as the bowl vent operates correctly (opens at curb idle, closes above curb idle) its exact degree of opening has only very minor effect on how the engine runs.

Is this possibly why there have been so many idling problems for the Holley 1920?
Click to expand...

No.
 
the bowl vent stays open at idle to feed it and closes with throttle opening, as fuel psi builds the vent closing keeps the fuel from possibly spilling out, let alone the psi is pushing and being drawn just fine rpm.at idle a siphoning effect
these carbs are a decent/basic design for the era they came about.
 
1wild&crazyguy said:
the bowl vent stays open at idle to feed it and closes with throttle opening, as fuel psi builds the vent closing keeps the fuel from possibly spilling out , let alone the psi is pushing and being drawn just fine rpm.at idle a siphoning effect
Click to expand...

No. There is no siphon effect or liquid fuel involved with the external bowl vent. If there's liquid fuel coming out of it, there's something the matter with the carburetor -- stuck inlet needle, stuck or sunk float, improper float adjustment. The fuel PSI also does not build with increasing engine RPM; it is a function of the fuel pump mainspring, not engine speed.

It's there to prevent flooding under heat-soak conditions after the engine is shut off. Once there's no longer air flowing through and past the carburetor because the engine's been shut off, its heat rises (naturally), which heats up the fuel in the carburetor. If not for the external bowl vent, fuel vapours would enter the intake tract via the internal bowl vent and other bowl-to-throat passages. This would make the engine hard to restart. So an external vent is provided to allow the vapours to escape -- to atmosphere through '70 ('69 in California); to the crankcase in '71 (and '70 in California); to the charcoal canister starting in '72. If the bowl vent hangs open above idle, you have atmospheric pressure rather than carb throat pressure levels above the fuel in the bowl, which can in some cases upset the carb's metering and cause poor fuel economy.
 
I was reading through some other Holley threads. One reader mentioned that the fuel pump or some part of the fuel line could have a crack that opens up when hot. This would allow air to be draw in to the fuel. The needle valve is not designed to stop air from passing through. Aerated fuel will also not support the float properly. The net result is that fuel would pass out of the vent.
 
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