Slant 6- Idle and Running

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Silum

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I've read through a number of people with similar issues but mine seems to be slightly different, I apologize if anyone thinks it was too close to other peoples questions...

The Car is a 72 Duster with 225, 1920 carb, just been picked up. I am trying to diagnose without throwing too many parts at this motor. So far I've replaced all vacuum lines and have a balast resistor and ignition coil in the mail since they are cheap. Car had old gas it in when I got it and didn't have a fuel filter either, both of those rectified.

Problem... Car won't idle without some throttle. The car turns over and starts, once started it will run with light throttle and sounds healthy...until warm. It won't stay on unless there is light throttle, if I try to give it more throttle, it stalls like its not getting fuel. Once the car warms a little, it stalls and will not start. The choke seems to operate fine, except once its open/cars warm; the car stalls and will not start. Strong smell of fuel throughout all of this but it's not exactly acting rich either. I can't tune the carb well because I can't get the car running long enough, but changes I do make to the idle mixture and idle speeds don't much of a difference (even extreme changes). One thing is the fast idle screw and cam seems extremely 'loosey goosey' with lots of slop, are there any photos/videos out there showing how the 1920 linkages are all meant to operate as it's hard to tell if mine is correct.

Balast resistor faulty?
Faulty carb float?
Carb problems, in need of a rebuild after some varnishing from old gas?

Thanks in advance for you help!!

TLDR: Slant 6 only starts from cold and wont idle well, cant gain revs without stalling, once warm it stalls and won't start.
 
Sounds like the carb is a POS. I would imagine it needs a kit at best, maybe a float, too. No way to know for sure since I'm not standin there.
 
It's not your ballast resister. Probably not your carb float, either, but your carb is going to need some attention.

Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download. Also see Tune-up parts and technique suggestions in this post, and pay careful attention to the valve adjustment.
 
Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download
*Sorry to highjack the thread
I just want to say @slantsixdan I read that post over and over about a year ago when I first got my valiant and it was a huge help. So much good info... And I had a gut feeling I was in the right spot when I read "... so don't follow advice that starts and ends with "Set the mixture screws two and a half turns out" ... Anyway... @Silum good luck chasing down your issue, sorry I don't have a silver bullet answer for ya but I'm still wrapping my head around all this stuff... Definitely check out those links.
 
The 1920 has a weird economizer block in the fuel bowl that can get plugged up. Take it out and soak it and hi the passages with air to clean them out. I bet its there. Part #44. Also check the throttle shaft for wear. The accelerator pump sort of works backwards on that economizer plate and if it has a leak, it will weep fuel out the linkage or worse, a small hole that will shoot fuel onto your intake.
Holley1920CarburetorExplodedDiagram.jpg
 
Thank you all, I have a few things to try then. Thank you Dan for the resources, the 1920 guide was exactly what I was looking for.

I can do valves but I see it needs a nicely warmed up engine to be accurate, I can't really get there (I get about a minute). The car purrs when I have it on the throttle during those first few cold moments so I would surprised, but I get the logic as it expands. I will look at the economizer plate, perhaps a rebuilt kit will get my more familiar with the thing as I go through that process so I may start there too.

This is early days for me and I usually get to grips after finding out everything not to do. It's nice to have a direction to point my grubby hands to! Thanks again.
 
Nothing wrong with setting the valves cold. Just do it a little wider, like .011 and .022
 
Thank you all, I have a few things to try then. Thank you Dan for the resources, the 1920 guide was exactly what I was looking for.

I can do valves but I see it needs a nicely warmed up engine to be accurate, I can't really get there (I get about a minute). The car purrs when I have it on the throttle during those first few cold moments so I would surprised, but I get the logic as it expands. I will look at the economizer plate, perhaps a rebuilt kit will get my more familiar with the thing as I go through that process so I may start there too.

This is early days for me and I usually get to grips after finding out everything not to do. It's nice to have a direction to point my grubby hands to! Thanks again.

You don't have to adjust the valves running or hot. People have been making those adjustments since the beginning of the internal combustion engine cold. Just add .002" to the cold spec and you're right on the money. No burned hands and no flying tools. I've done it both ways and there's no difference. No need to risk injury.
 
You don't have to adjust the valves running or hot. People have been making those adjustments since the beginning of the internal combustion engine cold.

The slant is the first engine I've come across where the manufacturer recommended a hot adjustment. Granted most of my valve adjustment experience is with European stuff, but even the old Fords I've messed with gave a cold spec only.

Plus, how are you going to get a brand new engine hot to set the valves the first time? Aim a blowtorch at it?
 
The slant is the first engine I've come across where the manufacturer recommended a hot adjustment. Granted most of my valve adjustment experience is with European stuff, but even the old Fords I've messed with gave a cold spec only.

Plus, how are you going to get a brand new engine hot to set the valves the first time? Aim a blowtorch at it?

LOL. Good analogy.
 
Ha, well that comment went down a treat. I'll try to find some time to do valve lash. I'll get back to you all when that is done and we'll see.

Thanks again! ...ordering a blowtorch now.
 
UPDATE

I focused on the economizer plate, following pishta's advice. Cleaned everything out (it was gross, so I'm guessing a rebuild is still needed). The car fired up and idled great, enough for me to do some tweaks. Now allows me to throttle up and sounds great! Thank you pishta!!

That's the good news! Bad news is it still dies as soon as it get's warm. Will start on a valves once I get my valve cover gasket in. I don't really have any back up options after that. She'll get a good tune up and I'll do a compression test while I'm at it but if its not the valves, I don't know what it is.
 
adjust idle speed on choke and off choke. 2000 RPM fast idle (choked) 750 (800 for 198 CID) hot idle. Yours is a type III choke setting: 2nd step in figure 5. Make sure choke pulls all the way off when warm too.
upload_2020-6-9_21-58-32.png
 
adjust idle speed on choke and off choke. 2000 RPM fast idle (choked) 750 (800 for 198 CID) hot idle. Yours is a type III choke setting: 2nd step in figure 5. Make sure choke pulls all the way off when warm too.
View attachment 1715543712
Ok thank you for that photo, that I have tried to do but I feel like there is a lot of play in where the fast idle cam sits on the idle screw. I will try to get a video to show what I mean, but it may well be normal. Am I doing this adjustment with the car running? I've been trying to set fast idle with the engine warmed but off and the throttle opened to 20 degrees, setting it onto that 2nd step.

With the car fully warmed up should it remain sitting on that 2nd step at idle? Because it doesn't. :( I can try doing this adjustment again with a running engine at least now though.
 
no, warm motor will cause choke to pull off that step once you tap the gas pedal...its spring cocked like a gun. Once the bimetallic spring is warm, that stepped cam will rotate right off that step to base idle once you tap it. (itll stay on that forever if you dont tap the gas). Once the cam is out of the way due to the choke being warm, it should rest on base idle, that's where you set your 750 RPM. If you want to do it manually, just manually move choke off on a warming engine (manipulate choke rod while releasing that stepped throttle stop) It will be under a little spring pressure but that will relax when the choke spring is warm (you could actually heat the choke spring with a blowtorch and it would pull of just like a warmed engine, Id use a heat gun but manually doing it is easy). Those choke linkages get sloppy over time, dont expect them to be precision rotating. There is a bleed half way down the throat that leads to the mixture screw passage, make sure that is clear. Take mixture screw out and shoot carb cleaner into the bleed and see if it comes out the screw hole. Wear glasses! Return screw to light seat then back out 1.5X for baseline. Might want to make sure the throat is clear of sludge where the butterfly hits the venturi also.
 
no, warm motor will cause choke to pull off that step once you tap the gas pedal...its spring cocked like a gun...
Since I can now make changes with the car on, any change to the fast idle screw seems to cause it to stall, and by that token, any manual change to the choke causes it to stall. I'm still getting strong fuel odor.To be clear then, I am setting the fast idle cam with a cold motor and the engine off? Since the choke would be fully open and it's meant to no longer be sitting on the fast idle screw?

Made sure the mixture screw passage is clear, it is.

Was going to do valves today but didn't realize there wasn't a crankshaft bolt to turn, then I decided I would take out the spark plugs and do it by hand, and realized it wasn't a 5/8 plug. Can't catch a break ha! Will get there eventually.

I'm thinking more and more it is the carb. When warm, the car will start and run great IF I manually hold the choke closed a little, or a lot. With the car on I played a lot with the fast idle screw to see if I can create a situation where it would idle without holding the choke shut, I couldn't. Also, the regular idle screw is almost completely screwed in, otherwise the rpms are too low to keep it running. I've tried adjusting idle mixture, again this really doesn't change much.
 
sounds like you may just want to start with a known good carb, many here. Heck I got one if you want to come over this week and pick it up to try. 5/55 Fwy Tustin. Could be a hot vacuum leak? Pinch off all the vacuum lines including the advance and let it warm up. see if it will drop off choke onto base idle and idle. Hmmm, you said it will idle with the choke actuated slightly.....?
 
sounds like you may just want to start with a known good carb, many here. Heck I got one if you want to come over this week and pick it up to try. 5/55 Fwy Tustin. Could be a hot vacuum leak? Pinch off all the vacuum lines including the advance and let it warm up. see if it will drop off choke onto base idle and idle. Hmmm, you said it will idle with the choke actuated slightly.....?
Well I may end up taking you up on that offer! Im in Mission Viejo so pretty close. I have a rebuild kit on its way so I will start with a thorough clean and rebuild first.

Yep, with the choke actuated slightly, it'll idle all day.
 
Well the plot thickens...

Two photos attached (One is the thing I bypassed, one is the awful intake manifold connection)

I disconnected this (sits on top of the valve cover, it is OSIC? My slant is a 72 so I'm not sure what it is), but it had a hose disconnected anyway (the one pointing forward). It used a T and connected to the carbon canister, the distributor vacuum advance, and the carb. I bypassed it and connected the vacuum advance line directly to the distributor.

The car ran better. It would now run even with the choke fully disengaged*. The car now runs when warm with even partial throttle, but STILL wants to stall without any throttle. I can also still manually choke the engine and keep it running.

I'm showing a photo of what it looks like at my intake manifold. I am sure that could be leading to a vacuum leak (as well as a fuel leak!). This could be causing my problems also. New gaskets are coming. Lots to do.

20200611_112425.jpg


20200611_112350.jpg
 
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I did not unplug it no, just bypassed it's vacuum lines. I wasn't even sure it was the OSAC and can find almost no information on it. Should I?
 
Here's where everything was going, for whatever this is. Im assuming OSAC based on what that does and where it is positioned.

20200611_112425.jpg


Edit: Is this the OSAC valve? - Slant Six Forum this explains what it is. It is a CA car. I wonder if it still has anything to do with my problems though.
 
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I believe its called a solenoid delay valve- CA emissions stuff- not sure if you can just unplug it or if its better to just use vacuum plugs on it.
 
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