1977 Chevy Blazer Failed Smog Test High CO

It seems your Chevy Blazer is running very rich. The right way to adjust the carburetor is by using a 5 gas analyzer or a BAR-97 smog machine. Adjusting the carb via the mixture screws by "number of turns" or by listening to engine misfires will do no good when it comes time to smog check. Fine adjustments are needed in order to set 14.7:1 air/fuel ratio. By using a gas (exhaust) analyzer you'll be able to accurately adjust your Blazer's carburetor to get passing smog check results.

If you feel the carburetor is not the cause of your Blazer's high CO fault don't forget to look at the basics like engine compression and/or possibly any condition which can introduce fuel to the intake manifold bypassing the carburetor, such as a faulty EVAP system.

You may also consider rebuilding your Chevy Blazer's carburetor. However keep in mind that to will require fine tuning. Often times vehicle owners assume that a carburetor rebuild shop will adjust the carburetor prior to returning it to the owner. The carb rebuild shop can not fine tune a carburetor until it has been installed on the engine it came off of. Only then will they be able to, using a gas analyzer, measure the amount of HC and CO the engine is producing based on the carburetor high and low adjustments.