Just when I think I have my carb dialed in, I don't

[MisterB]

OK, guys. Before I did anything else I wanted to do a video of me starting and idling the truck stone cold with the air filter on. You'll notice at about 45 seconds, it kind of stumbles and idles rough for a bit and then the idle increases and it smooths out. The high idle setting stayed on even though the engine was warmed up to normal temps, and didn't come off until I blipped the throttle.

Please stick with the video and let me know if I need to adjust the high idle screw where it hits the cam. I also obviously need to still figure out the stumbling from 45 seconds in to about 2 minutes. At least it isn't dying anymore, so I'm getting closer

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[88 diesel]

I can't open your video. Blipping the throttle to get off high idle is exactly how it works so that's fine. Your tag under the hood or your book w give you high idle rpm.
If it were me I would now check my timing and timing chain slack. Check your accelerator pump function and make sure the fuel isn't flowing inside the venturi where it shouldn't. If all are good then let it warm up and set the idle and mixture.
I should have asked about cam profile as that will affect idle vacuum so I'm hoping it's stock.
Sounds like you got it zeroed in.
Bill

 

[Matt69olds]

Sounds to me like raising the fast idle would help. Do you have a tach you could temporarily install? Set it to about 1400-1500ish.

 

[MisterB]

I can't open your video. Blipping the throttle to get off high idle is exactly how it works so that's fine. Your tag under the hood or your book w give you high idle rpm.
If it were me I would now check my timing and timing chain slack. Check your accelerator pump function and make sure the fuel isn't flowing inside the venturi where it shouldn't. If all are good then let it warm up and set the idle and mixture.
I should have asked about cam profile as that will affect idle vacuum so I'm hoping it's stock.
Sounds like you got it zeroed in.
Bill

This truck had a frame off restoration and repaint, so all the stickers are gone.

Have you tried the video again? Seems to be working fine.

That's good news about the high idle needing to be manually turned off by blipping the throttle. I thought I had heard some folks saying eventually high idle would creep back down on its own.

I honestly don't know the first thing about checking timing. I don't have a light for that and the videos I've watched look like I might make it worse lol.

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[MisterB]

Sounds to me like raising the fast idle would help. Do you have a tach you could temporarily install? Set it to about 1400-1500ish.

I don't have a tach (or a temp one), but I can't imagine having the idle set much higher than it is. Seems high already. Were you able to get the video to play, and hear my fast idle?

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[MisterB]

I can't open your video. Blipping the throttle to get off high idle is exactly how it works so that's fine. Your tag under the hood or your book w give you high idle rpm.
If it were me I would now check my timing and timing chain slack. Check your accelerator pump function and make sure the fuel isn't flowing inside the venturi where it shouldn't. If all are good then let it warm up and set the idle and mixture.
I should have asked about cam profile as that will affect idle vacuum so I'm hoping it's stock.
Sounds like you got it zeroed in.
Bill

Also, not sure about what cam it has. If it's like how everything else was built on this truck, I would assume the cam is different from stock

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[88 diesel]

It's not a stock cam. The high idle is way too high by 3-4 hundred. Bring that down as low as it will stay running. 9-12 hundred should be good. It's hard to tell how it will idle w that cam profile.
That isn't your papa's 350 lol
That will always be a cold blooded engine. Stop trying to change it and embrace it for what it is. Sounds strong. Somebody spent some money on it. Never let it sit and idle for long periods. It will flatten a lobe. Make sure it has good oil pressure at idle. That might dictate your idle speed at normal temp. Throw out the book on most everything regarding idle and timing.
Wish we were closer I'll bet that puppy runs.
Bill

 

[MisterB]

It's not a stock cam. The high idle is way too high by 3-4 hundred. Bring that down as low as it will stay running. 9-12 hundred should be good. It's hard to tell how it will idle w that cam profile.
That isn't your papa's 350 lol
That will always be a cold blooded engine. Stop trying to change it and embrace it for what it is. Sounds strong. Somebody spent some money on it. Never let it sit and idle for long periods. It will flatten a lobe. Make sure it has good oil pressure at idle. That might dictate your idle speed at normal temp. Throw out the book on most everything regarding idle and timing.
Wish we were closer I'll bet that puppy runs.
Bill

Thanks for the input. I'm not trying to change it, per se. It's just that since getting it, I have replaced plugs, wires, cap, rotor, added K&N, fuel filter, thermostat, and on and on. I wanted to make sure the carb was dialed in after all of that so I was maximizing fuel economy and drive ability. At the same time, Temps have dropped and so I felt like I needed to check things. I connected it to a vacuum gauge, and it was in the red zone, which says timing could be off, so I adjusted idle and both fuel mixture screws until it was in the green zone and ran well. I just have that first couple minutes of cold idle to sort out, and I should be good

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[88 diesel]

Sweet sounding engine

 

[MisterB]

Sweet sounding engine

I decided to bump down my idle when it's in park and warmed up by just a tad, and then I turned the high idle screw two turns to the left, so we'll see how the effects things tomorrow morning

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[Matt69olds]

I don't have a tach (or a temp one), but I can't imagine having the idle set much higher than it is. Seems high already. Were you able to get the video to play, and hear my fast idle?

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I did watch the first 2 minutes of so, I based my suggestion on the engine sound at the 1:35 point, when you first showed the tail pipe. To me that sounded like base idle, and I never saw you hit the gas, or blip the throttle from under hood. I watched more of the video, and later on it was obviously running much faster.


It sounds to me that the engine is loading up (I’m guessing that’s why it idles a bit rough shortly after starting, and then idles much faster once it warms up). I would try this: remove the air cleaner. Start the truck like you normally would. Immediately go to the carb, when the engine starts to idle funny, try opening the choke plate by hand, just a little. If the engine smooths out and idles faster/better, then you will know for sure the engine needs less choke. If opening it makes no improvement or makes things worse, try closing the choke flap. At least this way you will know what the engine wants, then maybe we can help you figure out how to tune the engine so I has what it wants.


I believe those edelbrock carbs are based off the Cater AFB carbs used on lots of mopars. I’m going to guess they had a choke pull off? I find it hard to believe the Chrysler corporation would hav built millions of cars and trucks that
had lousy cold start drivability. Maybe you could adapt a choke pull off to your carb?


Last idea, do you have a tuning manual for that carb model? If all else fails, read the instructions!!

 

[Colin]

An Edelbrock carb on a Holley intake... Hmmmm.

I know. I'm just no help when it comes to carbs,

 

[MisterB]

I did watch the first 2 minutes of so, I based my suggestion on the engine sound at the 1:35 point, when you first showed the tail pipe. To me that sounded like base idle, and I never saw you hit the gas, or blip the throttle from under hood. I watched more of the video, and later on it was obviously running much faster.


It sounds to me that the engine is loading up (I’m guessing that’s why it idles a bit rough shortly after starting, and then idles much faster once it warms up). I would try this: remove the air cleaner. Start the truck like you normally would. Immediately go to the carb, when the engine starts to idle funny, try opening the choke plate by hand, just a little. If the engine smooths out and idles faster/better, then you will know for sure the engine needs less choke. If opening it makes no improvement or makes things worse, try closing the choke flap. At least this way you will know what the engine wants, then maybe we can help you figure out how to tune the engine so I has what it wants.


I believe those edelbrock carbs are based off the Cater AFB carbs used on lots of mopars. I’m going to guess they had a choke pull off? I find it hard to believe the Chrysler corporation would hav built millions of cars and trucks that
had lousy cold start drivability. Maybe you could adapt a choke pull off to your carb?


Last idea, do you have a tuning manual for that carb model? If all else fails, read the instructions!!

Success! This was the final small detail that needed to be sorted out, and I think it fixed it.

I started it just like yesterday, and as it started to stumble and idle rough, I slowly opened the choke manually. As I did this, it smoothed out. So, I loosened the choke adjustment cap on the side and spun it a couple clicks to the left (it's now all the way to the left, and maybe a click past that. The truck idles well, and also what I did yesterday with changing the high idle by turning two full turns to the left made it ride a bit lower on the cam, and now it isn't idling so crazy high. I've got pics of both areas

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[Matt69olds]

Great job, hope the carburetor gods continue to smile on you!

 

[MisterB]

Great job, hope the carburetor gods continue to smile on you!

They did, luckily. Started it this morning. Frost on the vehicle everywhere, it was so cold. Two pumps, fired right up. Idled nicely, choke opened and fast idle increased to a normal level. Let it sit for a short bit, blipped throttle to take it off idle and it sat there and purred.

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