idle issues
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Senior User
Joined: Jan 2012
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From: Phoenix AZ.
idle issues
Hi first off new member love the sight, second I have a 1977 F-250 with a 460 with a C-6. I have a Carter 620 CFM carb on top of the cast iron stock intake. I have only had the truck for a short period of time and have been fixing all of the stuff previous owner ( who didn't have a clue ) rigged up. When I bought the truck it had problem idling, accelerating and problems that make you think carb is junk. So I bought a rebuilt one from respectble carb guy in the area. Now it it runs butter but first it idles same way more less it idles high but when i adjust it down it starts running bad so the idle need to be high in order to stay running in gear. Do I have a vac leak somewhere. I have used carb cleaner to try to locate it, although I need to check around EGR valve or maybe the seal around the intake manifold. Do you guys think it might be something else it also diesels when I shut it off but that could be from having the idle high. PLEASE HELP
Thank you
Thank you
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
Welcome to FTE!
A vacuum leak is a strong possibility. The intake manifold, carburetor base and power brake booster (if equipped) are areas to look. Don't bother with the EGR valve as it does not receive vacuum at idle. Note that it might not be possible to find a vacuum leak unless you lean the engine out so much that it barely runs. Once you clear the engine of vacuum leaks, set the mixture with a vacuum gauge. This is the proper way to dial in the mixture 100%. The vacuum gauge will also help identify the underlying issue.
I agree that the dieseling is likely a result of having to keep the idle speed so high.
A vacuum leak is a strong possibility. The intake manifold, carburetor base and power brake booster (if equipped) are areas to look. Don't bother with the EGR valve as it does not receive vacuum at idle. Note that it might not be possible to find a vacuum leak unless you lean the engine out so much that it barely runs. Once you clear the engine of vacuum leaks, set the mixture with a vacuum gauge. This is the proper way to dial in the mixture 100%. The vacuum gauge will also help identify the underlying issue.
I agree that the dieseling is likely a result of having to keep the idle speed so high.
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