hey guys, I just went to try to pass emissions in my 75 chevy, I just bought it from a member of the board and i need to transfer title and registration but they wont let me do it without it getting emissions tested.. So i took it down and it passed everything but the CO idle reading.. heres the info on the first run
loaded Standard
Hydrocarbons 116 350
Carbon Monoxide 1.99 3.00
Idle Standard
Hydrocarbons 350 350
Carbon Monoxide 7.44 4.00 FAIL....

Thats the first run, Ok, so after i pulled out, i went down the street and turned the idle mixture screws all the way in then back out 1 full turn, and i also pulled the timing back a little bit..




[This message has been edited by 79CamaroZ28 (edited March 17, 2005).]

Heres the 2nd run.. The engine was a little hotter because i hadent turned the fans on while in line.. It was around 200..

Loaded Standard
Hydrocarbons 146 350
CO 6.31 3.00 FAIL.

Idle Standard
Hydrocarbons 187 350
CO 4.00 4.00

Can youguys tell me what i did wrong.. Did turning back the timing hurt the readings maybe?? Should i just have turned the screws in and not touched the timing??? Thanks guys.. Nate

BTW< this is a 75 chevy 4x4, no cats needed...

Try backing the timing off more. That is one cause of a high CO reading.

Nate,

- Change the oil.
- Seat & take the mixture screws out 1.75 to 2 turns out.
- Ensure the PCV is working properly (hit it with some brake or carb cleaner while the eng. is running).
- Set ign. timing to 8 to maybe 10 before.

...and you should be good to go.

Edit: Yeah, keep the fans on. http://www.nastyz28.com/ubb/wink.gif

[This message has been edited by AZ_70ss (edited March 17, 2005).]

If you still fail, try going down two sizes on the primary jets. Once you pass change nack to what you like to run.

Jon

Hmmm, unlss things changed, excess CO is a rich mixture. A dirty air filter is the most obvious cause. I don't think you would want to retard the timing. Set at recommended setting for the engine, typically around 10 btdc.

For your idle adjustment you'd want the screws in as much as you can without a misfire, which would cause your HC's.