Carb settings help
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Senior User
Joined: Jul 2003
Posts: 124
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From: Cedar Rapids, IA
Carb settings help
Saw a previous post about setting timing with a vacuum guage, which got me thinking about a problem I always have. I don't know the proper procedure to adjusting my idle mixture screws and fast idle. I now have a vacuum guage and would like to try it myself.
I have a '74 F250 with a 460 and an Edelbrock aftermarket carb (I think it's the 1407). I put an electric choke on it a few years ago and thought I had set it correctly based on the instructions, but I've never been able to set my idle correctly, or my fast idle now that it's frigid outside.
Can anyone provide a step-by-step procedure for using a vacuum guage to setting my idle/fast idle/electric choke that a novice like me can understand? I think the current settings are close, but still not correct.
Thanks for the help
I have a '74 F250 with a 460 and an Edelbrock aftermarket carb (I think it's the 1407). I put an electric choke on it a few years ago and thought I had set it correctly based on the instructions, but I've never been able to set my idle correctly, or my fast idle now that it's frigid outside.
Can anyone provide a step-by-step procedure for using a vacuum guage to setting my idle/fast idle/electric choke that a novice like me can understand? I think the current settings are close, but still not correct.
Thanks for the help
Senior User
Joined: Feb 2006
Posts: 479
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From: Sonoma, CA
With the truck warmed up, connect your vacuum guage to the port in the intake manifold. You should also have a tach connected to see the idle speed. Adjust the idle screws slowly in until the idle starts to go down and the vacuum goes down. Now slowly back out the idle mixture screws until highest vacuum is achieved. Both screws should be set the same number of turns open. Now adjust your idle speed to the correct setting using the screw on the throttle linkage. Do the idle mixture again with the vacuum guage now that the idle speed has been adjusted. Your going for the highest vacuum you can get. Now, turn the screws in enough to drop the idle speed by about 25 rpm otherwise you'll be a little rich. Then adjust the idle speed to the proper setting. I do my fast idle by manually setting the carb to that position on the fast idle cam, and check it with my tach. Adjust as required. It's not quite as scientific.
Mine's a '76 F250 SC with a 460 and a Carter AFB just like the Edelbrock.
Good luck.
Mine's a '76 F250 SC with a 460 and a Carter AFB just like the Edelbrock.
Good luck.
New User
Joined: Jan 2008
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A vacuum gauge is more for setting idle mixture.. Not fast idle.
Before you do any Mixture type adjustments make sure all the mechanicals are set correctly
For fast idle ...Make sure your choke is indexed to spec
Before you do any Mixture type adjustments make sure all the mechanicals are set correctly
For fast idle ...Make sure your choke is indexed to spec
Last edited by Mil1ion; Feb 2, 2007 at 01:34 PM.
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Senior User
Joined: Jul 2003
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From: Cedar Rapids, IA
Tractoman, thanks for the step by step, it really helps. Looks like I'll need to also get a tach guage before doing this to make sure I set it correctly.
Do you happen to know what the regular and fast idle rpms should be set at?
Do you happen to know what the regular and fast idle rpms should be set at?
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