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Slant 6 carb issue

Timmayy

Timmayy

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I've been working on my newest toy that I bought last year. The last real issue I'm having is the 1 barrel carb. It's a 65 Dodge and pretty much original. I got it to a point where it's running pretty good. I leave it to a good friend to really fine tune it. He knows his stuff, really old-school. Any way, it's been at his shop and we order a new rebuilt carb (a couple of issues there but it's been resolved) Anyway the /6 runs great but when the choke fully disengages when it's warmed up the car starts to idle rough. Now he put in a new pcv valve, made sure that's not an issue, distributor is electronic so no points. When he puts his hand over the throat, it idles smooth again. He's tried everywhere to find a vacuum leak and no go. Now he's thinking that maybe the valves are adjusted too tight. They don't make a sound and purr like a kitten. The valves seem to be the last thing to try.
Anyone have any other ideas or does the valves sound like the issue?
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If no vacuum leaks it still sounds like the carb. Rebuilt carb might mean the float level wasn't set correctly.
 
He thought of that too but it's the third carb he's tried.
 
Spray around the manifold for vacuum leaks. Make sure the vacuum advance is working.

If all three carbs were rebuilt ones it still could be the float setting.
 
The combination intake/exhaust gasket may be the problem and can easily be missed. The strange triangle washers are designed to allow expansion/contraction.Meaning the intake/exhaust manifolds move every time the car engine warms up and cools.After 50+ years chaffing happens.Even if the gasket has been changed in it's life time.
I bought a 63 Valiant and the gasket was so worn out it was paper thin.Just shootin' in the dark at this one.
 
How much slop is in the throttle shaft to carb bore? Doubt if most rebuilds would include rebushing it. I just ordered a new Daytona Universal 1 barrel (actually 2 for the Offy dual carb intake) Holley 1904/1940 clone for the Dart, not going to mess with the factory carbs, everyone says they were poor when they were new let alone 50 years old.
 
Sure sounds like a vacuum leak somewhere.
 
Sounds like the intake/exhaust is the leading offender.
But a couple suggestions:
Try putting a vacuum gauge on it.
Does it have power brakes? Booster leaking?
How does it respond to the idle mixture screws?
How far out are they?
 
If you put your hand over the carb (essentially choking it) and it smooths out it sounds like its otherwise running on the lean side
 
He's done the mixture adjusting, sprayed everywhere for leaks. No power brakes. There is a new manifold gasket that the previous owner doubled up on for some reason but he can't find a leak there. We also thought of all 3 carbs having bad float adjustment. He's trying to get a hold of a technician from the rebuild shop to ask about that.
 
I believe the original carb was EITHER a Holley 1920 or a Carter BBS. The Holley has a vacuum operated power valve with the valve located on the right side of the metering block. The idle air is thru a fixed restriction on metering block and air horn. The idle fuel feed is thru the metering block to the down channel in the body leading to the external idle mixture screw. There is s gasket under the metering block.
The Carter BBS uses a fixed metering jet and a single step up metering rod vacuum opersted. Just about all /6s I've seen used the Holley 1940. Fuel level is important but not real critical...if you're close it'll be Ok. One step richer on the main jet.
On my /6, I ran the valves: I = 0.012" and E = 0.015" BOTH HOT engine OFF. I ran the timing @ 5° BTDC, take out the heavy spring, with vacuum advance connected and Champion N-12Y plugs at 0.032" and 750 RPM idle speed. YES, it's possible that the intake manifold at the head is leaking but in all my years I've not seen one leaking. Just my opinion of course.
BOB RENTON
 
Last edited:
Timmayy said:
He's trying to get a hold of a technician from the rebuild shop to ask about that.
Click to expand...

Last place you want to ask if they have the wrong settings. Specs get lost over the years on these old cars. See if the factory service manual has your settings.
 
Instead of using carb spray to look for vacuum leaks, take an unlit propane torch and direct the gas at the carb base, intake , pvc valve area, any possible area that draws a vacuum.
Reason why I like propane is you turn the valve on and go...nice and quiet , and you are not focusing on pushing aerosol button down. And its usually a little cheaper than carb spray.
 
Thanks for all the input. I am going over to his shop this morning with a valve cover gasket. I was going to change it anyway because of the old one leaking a bit so he is just going to check the valves to try and eliminate that possibility. He may pull the carb apart and just adjust the float himself. We were hoping to avoid that with a properly rebuilt carb but it may have to get done. I am going to pass this info to him.
 
Timmayy, Guys that mess allot with slants commonly double the gaskets(me for one) so it's not unusual to find.Till I started using RemFlex gaskets. Slants can be confusing and different.Maybe that's why I like 'um.
 
Darter6 said:
Timmayy, Guys that mess allot with slants commonly double the gaskets(me for one) so it's not unusual to find.Till I started using RemFlex gaskets. Slants can be confusing and different.Maybe that's why I like 'um.
Click to expand...
This is actually my first slant 6. I've had all v8s up until now. It's just a cool little engine to geek around town in.
 
I had a similar problem with the choke pull off arm assembly on my 66 Valiant. It would run great but once I put the air cleaner assembly on it ran like poo.
The choke pull off arm had been bent in the past and it was contacting the air cleaner. And from what I know they can't be adjusted or its near impossible to get them in the correct configuration again.
I had been adjusting out the problems with the arm assembly through the carb. Richening it or leaning it out I mean. Until I realized it was way out of whack due to the choke not opening and closing correctly.
Good luck!
 
Update. The valves are adjusted. No issue there. We are leaning towards the float adjustment. The problem is we can't take the carb apart until we get the OK from the parts supplier or else we are stuck with it once we open it up. He's called the 1-800 number of the supplier and no on gets back to him.
It runs great. Once it warms up is starts idling rough but pump the gas and it smooths right out. He puts his hand over the throat and it will smooth out the idle. We can't find a vacuum leak anywhere so It has to be something with the carb.
 
Timmayy said:
Update.
It runs great. Once it warms up is starts idling rough but pump the gas and it smooths right out. He puts his hand over the throat and it will smooth out the idle. We can't find a vacuum leak anywhere so It has to be something with the carb.
Click to expand...

This would point to a overly lean condition at idle, something is boinked up in that carb. Good Luck
 
69a100 said:
This would point to a overly lean condition at idle, something is boinked up in that carb. Good Luck
Click to expand...
Did you mention the carbs model and type? Is it Holley or Carter BBS? I may be able to help bettrr if I knew what type as esch had their own issues.....just a thought....
BOB RENTON
 
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