Rough Idle Problem- 1967 Valiant

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nixonrules

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I need some help troubleshooting a rough idle problem with my daughter's Valiant. It is a stock 225 with a Carter BBS. I have added electronic ignition to it some time ago. I pulled the plugs this morning, and all are the same- very light with a small amount of tan.

The symptoms are that it will run fine above about 1500 RPM, but as soon as it comes back down to idle, it will stumble, cough, and often die. The problem is worse when it's cold. I have to constantly feather the throttle to keep it running. It seems like it is experiencing a lean condition but I can't find a vacuum leak. Also, when it gets hot, it boils fuel over onto the intake manifold.

Here is what I have done so far:

1) Replace distributor and ECU (several weeks ago, it refused to start, and it turns out the pickup in the distributor was bad).
2) Set timing to 5 degrees BTDC at idle with vacuum advance unplugged
3) Disassembled and cleaned carburetor several times. Float is at 1/4". All other adjustments made per rebuild kit.
4) Adjusted valve lash to 0.010" Intake, 0.020" Exhaust
5) Checked plug wires for leaks/shorts
6) Checked coil per spec

I'm stuck. I've been working on newer cars for a while now, and think I've forgotten how to tune the old schools!
 
While idling put hand over carb opening- choke it. Does the engine speed up? This would indicate a lean condition, a carb problem/vacuum leak. Take a compression test. Tight valves?
 
Mine doesn't like the factory lash specs, but runs fine on .013/.023 after being warmed up.
On mine, the valve stems wore ruts in the rocker arms, and I had to make narrow feelers to fit in there so it would lash right. The slanty only fires three cylinders per revolution, so any compression imbalance shows up right away.
Other sources of trouble are;
>Slantys occasionally suck air right at the intake to head juncture.
>There is a gasket between the intake manifold and the exhaust manifold, under the carb, that occasionally leaks.
>the PCV, and/or its hose (which is specific to that duty),
>the Brake booster and/or it's hose, if you have one.
>and any device that is operated by manifold vacuum.
That said;
If your slanty has burned an exhaust valve the piston for that cylinder, at idle, with the throttle nearly closed, will suck exhaust back into the cylinder. You can actually feel this at the tailpipe, engine running of course, and assuming your system is reasonably sealed. Just put your hand over the tailpipe, not to shut it off, just to feel the pulses. When the bad cylinder comes around, it will fail to blow your hand off, and it will feel like it just sucked on your hand. Badaboom, you need a valvejob.

Now about that new ignition system..... Put a timing lite on her and watch the strobe-action, while you slowly bring the revs down from say 2000. The timing mark should smoothly move from an advanced number down to your base timing, without doing any stupid stuff; like adding strobes, missing strobes or seemingly jump the timing marks back and fourth.

Second last; check your timing-chain slack, by jockeying the crank back and forth against valve-spring pressure. It shouldn't move at all, but it always does. Just make sure it ain't more than a couple or so of degrees. If you find a lot od slack, AND the engine requires a lot of throttle to stay running, AND you have already changed the timing, it may be, that the chain has jumped.

Finally;
if your carb is puking gas, externally, it seems pretty obvious to me that the float valve system is not working properly, IMO you need to pressure test it.
However, if it is puking gas onto the throttle-blades at shut-down, and that gas is somehow finding it's way OUT of the throttle bores, that is a different problem, and points to the wrong gasket being installed during the carb-overhaul.
 
Last edited:
slantsixdan said:
Pull the PCV valve out the valve cover and throw a thumb over it. Now does the engine run below 1,500 RPM?
Click to expand...
Second that. I recently couldn't get my 1965 Dart w Carter BBD to keep running, no matter how I fooled with the carburetor. Finally found the PCV valve at the valve cover had a massive vacuum leak due to a rubber grommet which had fallen apart (Chinese rubber).
 
(clarifying: put a thumb over the end of the PCV valve, not on the valve cover)

…and since you mention the carburetor boiling over: by all means make sure the manifold heat control valve is working; verify the carb float adjustment, and do the do the fuel line mod, but you're reminding me of a case of an intake manifold with a crack in the plenum floor. This allowed exhaust into the intake tract—more of it when the engine was cold, less of it when the manifold heated up and pushed the edges of the crack together. Seen more often in certain aluminum intakes, but the case I'm remembering was an iron one. Caused symptoms like you describe.
 
Thanks for all the replies and tips everyone! Work got busy this week, and I haven't had a chance to look at this again until today. A few updates. After adjusting the valves, it did run noticeably better, but still would not idle without feathering the pedal- especially when cold. Also, it was definitely running lean. At idle, I could slightly close the choke and it would run smoother.

Last night, I pulled the intake/exhaust off and found that the exhaust manifold has a hairline crack on one of the exhaust runners that was starting to leak. I have several spares, so I am going to replace it today. Also got a parts carb that I'm going to go through today to see if it's fixable. All my spare exhaust manifolds are the newer type with the open choke stove area, so I'm going to have to see if that will work. I have the newer choke stove too, but it looks like it has a heating coil in it- not sure if I need to hook that up?

Also, to ensure no leaks at the manifold to head surface, I've always left everything a little loose, tightened the manifold to head nuts, and then the 3 intake to exhaust manifold bolts. Is that the right way to do it?

Anyway, we'll see how things go today. I will give an update once I have it back together and running. Thanks again! :thankyou:
 
The only factory choke thermostat that would work on a '73-up exhaust manifold with whatever pre-1974 carb you have is the one-year-only 1973 choke thermostat. This and the '74-up choke thermostats are non-adjustable, and their behaviour with or without the heat coil hooked up (which requires another piece, a modulator) is usually not what's needed. Save yourself a pile of hassle and get a № 1231 electric choke kit, which will drop right onto the '73-up exhaust manifold and hook right up to whatever carb you're running*, and provide easy adjustabilit (if you're running a '74 or later carb such as a Holley 1945, then the choke kit you need is a № 1234).

It is very much worth your while to get the good gaskets for the manifolds-to-head and intake-to-exhaust junctions.
 
I managed to get everything back together today, and fired it up without the choke linkage. It seems to be running fine and 100% better than before. I'll have to take it on a longer drive tomorrow to see if it acts up.

In the end, I swapped out the intake/exhaust manifold and carburetor. It took a little longer than expected because I had to fabricate an EGR block off plate, and rebuild the carburetor that was going on the car (which had mud dauber larvae in it with mud, spiders, etc). Very happy with it so far. Thanks for all the help!
 
Last edited:
nixonrules said:
I managed to get everything back together today, and fired it up without the choke linkage. It seems to be running fine and 100% better than before. I'll have to take it on a longer drive tomorrow to see if it acts up.

In the end, I swapped out the intake/exhaust manifold and carburetor. It took a little longer than expected because I had to fabricate an EGR block off plate, and rebuild the carburetor that was going on the car (which had mud dauber larvae in it with mud, spiders, etc). Very happy with it so far. Thanks for all the help!
Click to expand...
I wanted to provide one quick update to this. The car was running well, but still had a slight problem off idle when warmed up. It would hesitate, and sometimes pop and die- symptoms of a vacuum leak. I was finally able to determine that the vacuum advance diaphram was shot. I found a brand new distributor (chinese made) on ebay for about $70. I dropped this in and it fixed the problem.

They must have started re-popping the electronic distributors recently because I don't remember seeing them before.
 
Perhaps your new e-distributor is from Ningbo of China since they have long made one for the Chrysler V-8's. Those have an HEI ignition module on the side of the distributor (your's too?), thus termed "ready-to-run" meaning just needs IGN power. I have one on my 1965 273 engine. I recall some people found what ignition module they use. It is 4-terminal, like the original GM HEI module, but different dimensions. I recall for a Japanese car. I should research to buy a spare, though I'm thinking of using a GM 8-pin HEI module (1985-95) like on my other 2 old Mopars, especially if I change to an EFI system which can command spark timing (ex. Holley Commander 950 on my 1965 Chrysler). You can also now find some Chinese carburetors for classic cars, like the common Carter BBD, though I haven't seen a BBS yet. Many rant against Chinese-anything, often with reason, but the Ningbo products seem well-built.
 
BillGrissom said:
Perhaps your new e-distributor is from Ningbo of China since they have long made one for the Chrysler V-8's. Those have an HEI ignition module on the side of the distributor (your's too?), thus termed "ready-to-run" meaning just needs IGN power. I have one on my 1965 273 engine. I recall some people found what ignition module they use. It is 4-terminal, like the original GM HEI module, but different dimensions. I recall for a Japanese car. I should research to buy a spare, though I'm thinking of using a GM 8-pin HEI module (1985-95) like on my other 2 old Mopars, especially if I change to an EFI system which can command spark timing (ex. Holley Commander 950 on my 1965 Chrysler). You can also now find some Chinese carburetors for classic cars, like the common Carter BBD, though I haven't seen a BBS yet. Many rant against Chinese-anything, often with reason, but the Ningbo products seem well-built.
Click to expand...

It looks and feels exactly like the factory distributor. The only clue it's not is the 10mm bolt holding the position adjuster underneath. Also, it has a steel drive gear which is a nice touch. :)

www.ebay.com

New Distributor For Chrysler Dodge Plymouth 1973-1987 225cid 3.7 Straight 6-cyl | eBay

Product Type: Ignition Distributor; Condition: New; Country of Origin: CN.
www.ebay.com
 
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slantsixdan said:
Okeh, but why not just replace the vacuum diaphragm for a fraction of that price?
Click to expand...
I converted the car from points, and had bought a couple used distributors which were almost the same price as this new one. For just about the same price, I figured why not just get the whole thing new so I don't need to worry about shaft wear and who knows what else. This is my daughter's car, so my main goal is reliability.
 
slantsixdan said:
(clarifying: put a thumb over the end of the PCV valve, not on the valve cover)

…and since you mention the carburetor boiling over: by all means make sure the manifold heat control valve is working; verify the carb float adjustment, and do the do the fuel line mod, but you're reminding me of a case of an intake manifold with a crack in the plenum floor. This allowed exhaust into the intake tract—more of it when the engine was cold, less of it when the manifold heated up and pushed the edges of the crack together. Seen more often in certain aluminum intakes, but the case I'm remembering was an iron one. Caused symptoms like you describe.
Click to expand...
Had the same choke stove area crack in an aluminum 'E-beam' 2bbl intake. Tried in earnest to save that piece but ended up selling it cracked and cheap to a guy who TIG'd it and ran it. That intake weighed about 2 lbs! Wonder if a block off plate would have worked in warm So. Cal?
 
nixonrules said:
It looks and feels exactly like the factory distributor. The only clue it's not is the 10mm bolt holding the position adjuster underneath. Also, it has a steel drive gear which is a nice touch. :)

www.ebay.com

New Distributor For Chrysler Dodge Plymouth 1973-1987 225cid 3.7 Straight 6-cyl | eBay

Product Type: Ignition Distributor; Condition: New; Country of Origin: CN.
www.ebay.com
Click to expand...
No, the steel drive gear is not a nice touch. Chrysler knew what they were doing when they put a nylon gear on the distributor. With a steel gear on the distributor, if the distributor locks down....and I've seen it happen, now you take out the camshaft gear AND the oil pump gear. With a nylon gear, all you do is replace the distributor and go on down the road. I would no way ever run a steel gear distributor on a slant 6. Ain't happenin.
 
BillGrissom said:
Perhaps your new e-distributor is from Ningbo of China since they have long made one for the Chrysler V-8's. Those have an HEI ignition module on the side of the distributor (your's too?), thus termed "ready-to-run" meaning just needs IGN power. I have one on my 1965 273 engine. I recall some people found what ignition module they use. It is 4-terminal, like the original GM HEI module, but different dimensions. I recall for a Japanese car. I should research to buy a spare, though I'm thinking of using a GM 8-pin HEI module (1985-95) like on my other 2 old Mopars, especially if I change to an EFI system which can command spark timing (ex. Holley Commander 950 on my 1965 Chrysler). You can also now find some Chinese carburetors for classic cars, like the common Carter BBD, though I haven't seen a BBS yet. Many rant against Chinese-anything, often with reason, but the Ningbo products seem well-built.
Click to expand...
That 4 pin module is most likely a Bosch "021" ignitor. Cheap and common. This module is in my "ready to run" ECU-less LA distributor.
7952_4d40ced1a7f38.jpg

magnetic pickup...


Supercedes Bosch PNs
9-222-067-016 (9222067016)
9-222-067-017 (9222067017)
9-222-067-021 (9222067021)
9-222-067-024 (9222067024)


Pinout:
3 distributor
7 distributor
15 12V
16 Coil Negative
Case ground/earth
 
pishta said:
That 4 pin module is most likely a Bosch "021" ignitor. Cheap and common. This module is in my "ready to run" ECU-less LA distributor.
View attachment 1716092589
Pinout:
3 distributor
7 distributor
15 12V
16 Coil Negative
Case ground/earth
Click to expand...
I think that's the same module a lot of the Skip White distributors use.
 
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