1967 - 1972 F-100 & Larger F-Series Trucks Discuss the Bumpsides Ford Truck

Failed smog test at idle

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Old 08-07-2015, 12:44 PM
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Failed smog test at idle

Due to my own stupidity I need to have me truck pass smog to retain my classic vehicle status, I wrote down the wrong odometer mileage for my renewal.
I failed the idle CO test, I'm at 5.91% and needs to be no greater than 3.5%. High RPM test was fine just a problem at idle speed.
I interweb searched for information and have found two extreme opposites of what to do. Some say it's too lean and to open up the air/fuel screw. Some say it's too fat needs to be leaned out. Both of these can't be true? They are entirely opposite of one another! If the CO level is too high shouldn't I lean it out and even increase the idle speed? Right now my idle is at 500, I don't like high idles.
Any help for me is appreciated.
 
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Old 08-07-2015, 05:33 PM
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Smog test? what are you working on and specs please.
 
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Old 08-07-2015, 06:10 PM
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Smog test for the reason in my post
Truck is the one in my sig 71 f250 w/360
 
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Old 08-07-2015, 08:50 PM
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Check or replace all vacuum lines to the carburetor. If you have a timing light, set the advance at TDC. Lean the idle screws out as much as you can and raise the idle speed as high as you can get away with.
Talk your way into the shop with the tech. Play dumb. Have a screwdriver. Lean and raise the idle and spook the numbnuthz. You will pass.
Worked for me.

Semper Fi
 
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Old 08-07-2015, 10:43 PM
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And then as soon as it passes, retune it to make it run better.
 
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Old 08-10-2015, 05:48 PM
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As long as you don't end up with a Lean Fire Miss.
 
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