Emissions help (1 Viewer)

Sep 6, 2005
Boise, ID
I know this comes up all the time. I read through many great posts about fixes to pass emissions tests, but didn't see one with my exact problem.

I've got pretty low numbers on all the different tests except for CO at 2500 RPM. I was able to fiddle with the idle mixture screw which made my CO at idle decrease a bit, but that managed to raise my CO at speed reading even more. I'm currently more then double the limit. Heres the numbers:

2500 RPM:
CO - 10.12 (5.0 limit)
HC - 180 (900 limit)

CO - 3.66 (5.0 limit)
HC - 266 (900 limit)

Like I said I turned in the idle mixture a bit (3/4 turn), and also changed the air filter and did a little carb cleaning. This is on a stock '71. I do have a confirmed exhaust leak at the manifold, but I'm not sure if that affects this at all.

What's next? Any ideas why the idle numbers are good and the speed numbers are terrible?

Thanks for the help.

:cheers: Tim
Nov 13, 2005
Big Pine, CA.
Squinty20, it appears that your engine is running rich at 2,500 rpm. The CO (carbon monoxide) readings represent the air/fuel mixture at a given rpm. A higher CO reading means a rich fuel mixture. The idle mixture screw will have a minimum affect on the high rpm readings unless you REALLY screw it out.
Your high CO readings at 2,500 could be caused by a high carburator float level adjustment or some other carburator issue. If you have access to an emmissions analyzer, pull off a vacuum hose or two at 2,500 rpm and watch the CO's drop. Be carefull not to lean it out too much or your HC's will rise. Are you trying to pass a smog test??

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