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1979 5sp 928 project
 
Join Date: Apr 2012
Location: Boise Idaho
Posts: 199
Garage
Question on initial settings for a/f and idle...Does anyone have any tips '79 CIS

I have my car running now, but I can't seem to get it right and unfortunately i'm on a budget. I'd love just to take this down to a Porsche mechanic and say "here you go", but I don't have the money.

I know where the initial position for the the a/f mixture should be with the fuel pump jumpered I should just start to hear it whistle and then back it off until it quiets down.

How many turnes should the idle mixture screw be turned out initially? I have heard two, but just wanting to make sure.

The two adjustments seem to have an effect on each other and I need to know roughly where they should both start out at.

Thanks for your help

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1979 928 5sp project
1984 928S 5sp black on black
Old 06-24-2012, 03:41 PM
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Join Date: Dec 2007
Location: Sunny San Diego
Posts: 9,025
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The only way to really get it right is to have a wideband O2 sensor or some other way to get the A/F before the Cat.. CIS run a little rich on idle but you need to get as close to 14.7 A/F mixture at around 3K RPMs. I made the mistake at running my idle at 14.7 when it was leaning out at higher rpms. This destroyed my cat as well as my tailpipe tip.
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1981 Porsche 928 "Euro" Auto Gunsmoke Metallic Flat - Black Interior
1983 Porsche 928S "US" Auto Light Bronze (Copper) Metallic - Brown Interior **SOLD**
Old 06-24-2012, 06:20 PM
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Join Date: Oct 2005
Location: Owasso, OK
Posts: 386
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The number of turns will vary. Just make sure it is turned to lean then turn to rich (CW) until you hear fuel going through the injectors. This method works on a nonrunning engine. There is another setting technique for a running engine.

The reason the total turns will vary is due to the allowable variation in the control pressure.

Dennis

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Dennis
Old 06-25-2012, 04:49 AM
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