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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
Sorry, only use the info in the link for how a dwell meter can read duty cycle. That is a frequency valve on a GM carb motor, not CIS.

Found a better referance here on Pelican how it is done on an SC, we just need to get the right wires for the C2T: See part way down here: http://www.pelicanparts.com/911/911qa/911Q_misc2.htm

This is the meat of what it says:

" How do I set the mixture properly on my 911 CIS motor?
The procedure is to use a high-impedance (digital) dwell meter to measure the duty cycle of the CIS frequency valve. You can do this from the test connection inside the electrical panel at the left rear driverís side of the engine compartment. Itís the little black plug with a cap, near the CD box. Inside are three connector pins. Connect the positive lead of the dwell meter to the green/white wire pin, and the ground to the brown wire pin. When the engine is at normal operating temperature, the reading on the dwell meter should dither around 45 degrees (using the 4-cylinder scale), typically ranging from 40 to 50 degrees. This translates to 50 percent duty cycle, meaning that the frequency valve is on half the time, and that your basic mixture setting is good. (If you are lucky enough to have a meter that measure duty cycle, obviously you are looking for about 50 percent.)

If you see a higher dwell reading, say 70 percent, it means that the system is trying to control a basic mixture setting that is too lean. Conversely, if you see a low reading, say 30 percent, it means that the basic setting is too rich.

The mixture is adjusted using a special 3mm Allen wrench, through the hole between the fuel distributor and the rubber air duct. Turning this screw to the right makes the mixture richer, left makes it leaner. Never blip the throttle while the wrench is in the hole, or you may bend the air sensor plate. Also, you want to finish the adjustment by turning to the right.

All of the above assumes that you are working on a 80-83SC, with the Lambda oxygen sensor. Correct basic mixture setting helps smooth transition from cold start to warm running, and overall efficient operation."
Old 03-17-2009, 02:11 PM
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