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My take - CO

May 25 2008 at 11:42 AM
Mike Richmond 

Response to Another question about emissions test

I have passed CO standards of 2% with dual carbs.

NOx is caused by heat- ironically the more efficient your burn from a traditional point of view, the higher the NOx. In a car like yours, too much ignition advance will lead to too much NOx. Unfortunately, too much advance for NOx may mean just enough for the car to feel right. HC is usually a misfire.

If memory serves, air injection was used to reduce HC and CO. But as I said, you can get a Weber lean enough to pass without air injection.

Here is what I would do. Make sure your choke is opening all the way. If necessary, lock it open if it seems like it wants to flop closed after warmup.

Make sure the air cleaner is clean.

Make sure the throttle plate really closes when the the throttle pedal is up.

Adjust the idle mix to the point where the engine just starts to miss at idle, then back off just a hair. This should raise your unburned HC and lower your CO.

Try advancing the static timing. This will raise your idle speed which you should then back down on the carb, then you should be able to lean the mix a bit more. This will lower your CO while raising NOx and HC.

In other words use the headroom you have on NOx and HC to get your CO down.


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