Peter F

Can i adjust the CO myself and get it fairly ok?
Need advice of procedure.
Or is this a must do at a garage with proper measurment equipment?

Sean79 5spd

You can do it yourself and get fairly close. Below is an excerpt from an article I have (not sure where I got it from) Ignore references to where things are as this procedure was for a 911, process is the same
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With the engine at operating temperature (use the oil temp gauge), adjust the engine idle speed to specification (check the manuals, or the sticker in the engine compartment). The tachometer in the dash is accurate enough for this. The idle screw is located under the air cleaner on the throttle body - it is not very easy to locate the first time. You may want to take the air cleaner off or use a mirror to see it better. You need a long flat blade screwdriver brought in from the left (driver's) side.

Now, use the 3mm wrench to adjust the CO mixture. This adjustment is located in front of (towards the car's front) the top of the air cleaner box on top of the engine. Although easier to locate than the idle screw, it is not in an obvious location. Here again, a small mirror and flashlight may help. The adjustment control is located on the fuel metering unit (in front of the air cleaner, with all the fuel lines going into it).

With the engine idling, turn the 3mm wrench counter-clockwise until the idle speed makes a definite drop (by sound or the tach). Next, turn it clockwise until the idle speed increases again, and then continue slowly clockwise until it drops once more. Continue back and forth until you find the center of the range of highest idle rpm. For a 'pass smog' tune, turn the CO counter-clockwise (leaner) until the idle just starts to drop. for performance, adjust clockwise (richer) until just before the idle starts to drop. If the engine takes a long time to reach idle after you rev it up, it is a bit too rich - turn slightly counter-clockwise. It is best to adjust the mixture from lean to rich.

Good Luck.
Sean

hupp

Sean79,

Is this procedure possible while the car is running? I have always experienced stalling when adjusting the mixture screw. In order to make an adjustment, I must slightly depress the screw then turn. The car stalls when I depress because it moves the air sensor down.

jpitman2

It can take a light, quick touch to adjust this baby, having watched my wrench do it. It is pretty sensitive also - very small amounts of movement required.
jp 83 Euro S K-jet, CIS, whatever 46k mi

Sean79 5spd

Hupp, yes you do it while the car is running. As Jpitman says, light touch and small movements! Takes a little practice.

Joe Ricard

Just for reference the location of these components are not the same as the 911 procedure.

silver 78 5 speed

Peter F

Hi Sean,
thanks for the write up.
Will try and tune it tomorrow, will post result.

Cheers/Peter

Curt

Peter, I have adjusted my CO on my 79. I dont think you will be able to do it the same as the above write up. You are correct. You have to push down then turn. The engine does want to stall while doing this. There is a plug in the bottom of your cat. (if you have one) that allows you to hook up a CO guage. That is the only way your gonna set it perfect. On my 79 I swapped out the old cat and replaced it with a 87 dual in dual out cat. This cat had the O2 sensor in place. I extended the O2 wires up inside the car just under the shifter. im able to hook up my multimeter and take readings after the car is warmed up. The reading should be inbetween 0.500 and 0.700 volts. The lower the voltage the leaner it is the higher the voltage the richer it is. Trust me it is very touchy once you get it tuned down to 0.500 and 0.700 volts I was able to get mine to run at about 0.580 to 0.660 volts. The car ran better after making this adjustment. My car was running way lean. The car actually holds and idle now.

Sean79 5spd

I agree with Curt. The procedure above allows you to get fairly close to a correct setting but is a short term fix. Ultimately, you should have it set by a shop or use Curt's system.

Peter F

Ok,
but my car doesn't have cats at all.
So no O2 sensor to hook up to there.

V-Fib

There are several older air/fuel ratio analyzers (exhaust gas analyzer) out there. You have to look around, and if they are in good shape, still bring a premium. I bought one off Ebay, for $100.00 and it works great even on cars with carbs. There are also some newer ones in Summit and Jeg's catalogs that you hook up to an O2 sensor and it has a dash display. You do have to weld a bung in the exhaust for the sensor though. Good luck.



Anthony Tate
79/928 Silver Metallic

hupp

Anyone have the smog pump bypassed? If so, has this had any significant effect on your emissions? Also, disconnecting the smog pump line may provide a location for an O2 sensor -- that is if one is satisfied with the smog pump bypass.

Curt

Oh yeah, forgot to mention. Disconnect the smog pump before taking any CO readings. That is very important.

You can mount your own O2 sensor by drilling a hole in the exhaust just before the cat or where the two pipes connect. buy yourself an O2 sensor and find a nut that will thread on. Weld that nut onto your exhaust over the top of the hole you drilled. Then screw in the O2 sensor and run the wires up through and into the car where you can hook your multimeter up to it. The better the O2 sensor you buy the better results and readings you get. A three wire is best but they are the most expensive.