Tuning cis mixture
 

Recently purchased an '82sc semiproject. Although I'm mostly used to MFI, the CIS is pretty simplle as well...well sort of. After checking timing, and disconecting the Lambda Sensor, etc... I began adjusting the mixture. I've got it set so there is a significant power increase from when I purchased the car. The bad news is that when I rev it and release the gas pedal the rpm's overshoot down to about 3-500 rpm's and then back up to idle speed. It does idle very steady at 900 or so. When I adjust the mixture a little leaner, (counter clockwise) there is much less overshoot down past idle, but also less power. Any suggestions?

There is a round (about 1/2") test plug, with a cap, behind the engine compartment electrical panel. Look under the aluminum panel toward the CID unit. The test plug has three small round prongs.

Put your multimeter leads on the green and the brown prongs. Set to 4-cylinder dwell. The readings should bounce around, averaging 45.

Recently I unplugged my O2 sensor and the car runs smoother. An overly rich mixture can heat up your catalytic converter and wear it out or plug it.

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'83 SC

Are you "tuning" the mixture using CO% as a guide? My '78 3.0L was doing the same thing, and although I uncovered lots of other stuff, the mixture had a big effect on this.

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Michael
'78 911SC Euro

you really should use an exhaust analyzer. you will never know if it's set correctly without it. leave the oxy. sensor disconnected. they run better that way. set CO at3.5%. set timing at 35 degrees at full advance. idle at 1000. should fix your problem.

I will second what John said. You really need to set it with an EGA. The O2 sensor method with a dwell meter works, ok, but not was well. You also are assuming your sensor is working perfectly, and even then its approximate. I recommend disconnecting the sensor, but thats another topic all together. There are plenty of postings in the archives about that.

Nick.

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Nick Shumaker
1982 911SC Coupe
nickshu@yahoo.com
PCA -- Rocky Mtn. Region

[This message has been edited by Nickshu (edited 04-12-2001).]

Thank you all for your comments, I have been adjusting by "feel", so I guess I'll hook up the gas analyzer.