I went to get the emissions test on my 1982 F150 with 302 engine in Colorado. And as luck would have it when I got there, my engine decided to start revving (up to 1000 and 1200) when idling. It failed the emission test due to high CO levels but everything passed. When it's not idling it does sound a bit rough and can shake the car but being my first V8 truck I am not sure if that is normal.

If I screw in the idle adjustment its stops revving but the idle is too high (I will confirm the RPM that stops it revving when I get home).

When i bought the truck the previous owner who was going to restore it had put a new carburetor on the truck, my next move was to take a look at the idle mixtures screws (It's a 2 barrel carb) but wanted to see if anyone had advice on the next steps I should take. I did recently add some gumout (Complete engine cleaner) to the fuel tank and have probably done 30 miles with it.

 

High CO means you are running too rich which indicates an issue with your carb or a plugged up air filter.The idle screws will have nothing to do when they put the car on the dynometer and get the speed up. The high idle could be from a sticking throttle shaft or the high idle cam. You really need to get a Haynes or Ford service manual and follow the procedures on doing any adjusting of your carb.. When I used to take my old carburated cars for emission testing, I always went with a fresh oil change..

 

I was expecting to see two idle mixture screws. How do I adjust the idle mixture?

 

There is usually a tamper proof plug covering the screws. They are put there for a reason.You need to learn more about adjusting your carb.from the manuals I suggested. You may need special equipment to get everything set to specs.

 

There's 1 mixture screw, and there's a LOT more to the idle speed than just one stop screw. At this point, a reman carb might be a good investment, if you can find one that's guaranteed to be pre-adjusted properly. But I wouldn't let go of the current carb until the replacement is running right.

 

Wife had a 1981 T-Bird with a 302/variable Venturi carb that quit running right. Dealers recently retired carb expert came back in and rebuilt that carb twice without luck. Turned out the problem was a bad in line check valve in a vacuum line to the carb, not the carb itself.

Back then I usually rebuilt my own carbs,(still do). But that one was so different, and required special tools, I was afraid I would not be able to solve a problem. Glad that one went to an expert.

 

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