Help with CIS

[76911S]

I am looking for a little advice on adjusting my CIS. After not running my car for about a year, it now has a strange idle. The idle after warmup will very up and down almost as if the throttle peddle was being pushed in slightly every 10 seconds or so. Any thoughts on the best place to start?

Thanks in advance..

[Hladun]

Common CIS problem. Set the richness correctly.

[Doug Steinel]

Mine did that because the mixture was too rich. I turned the mixture screw 1/16 and the problem went away. Do you have any idea what the CO reading is?

[76911S]

No idea on the CO reading, I kinda thought that was a good place to start it seems to be running a little rich. I assume that I will have to reset Idle speed after adjustment richness?

Thanks again..

[Paulporsche]

This is a common rich condition. If you don't have a CO gauge, turn the mixture screw counterclockwise in 1/ 16 increments at a time.

And yes, usually when you lean out, you will have to lower your idle speed.

[Hladun]

For 76, 2 to 4% (airpump disconnected). But the adjustment is very sensitive so setting buy guessing is a very bad route.

[Paulporsche]

Hladun makes a good point. Using a gauge will give you a base figure from which to work. Each full rotation of the mixture screw is approx equal to 8%, so you don't want to turn it much each time.

Remember, if you try this adjustment and it doesn't work you can set back.

See the "advice on setting idle" thread for how to find your car's sweet spot.

If you are not comfortable doing this, a good wrench can set it quickly and cheaply.

[76911S]

Okay, so what is a CO gauge and where can I get one?

Thanks..

[Doug Steinel]

76911S,

CO stands for "carbon monoxide" one of the base parameters in the exhaust gas which can tell you if your air/fuel mixture is correct. It is checked, like the other exhaust parameters, using an exhaust gas anlayzer. Many guys here buy them for about $375... but I see used ones go in ebay fro $150 all the time. I bought one on ebay last month for $150 and it is fine. With that diagnotic tool, you can start turning away on that mixture screw. My CIS car runs best with the idle mixture at 3% though that would fail most states' smog test. You can set it at less than 1% for the test, then turn it back to 3%.

[Doug Steinel]

Paul,

How do you know that one complete revolution of the mixture screw changes the CO by 8%?

[unclebilly]

Don't set it yet. Clean the mechanism with carb cleaner first. If it was OK before sitting, it should still be OK once it is cleaned up.

Set your idle first and make sure you have no vaccum leaks.

After you get all the residue out of there, then set it if it needs it. You need a 3mm allen wrench. If you do have to set it, you'll probably only have to turn it 15° or so.

[mikester]

Originally posted by Doug Steinel
76911S,

CO stands for "carbon monoxide" one of the base parameters in the exhaust gas which can tell you if your air/fuel mixture is correct. It is checked, like the other exhaust parameters, using an exhaust gas anlayzer. Many guys here buy them for about $375... but I see used ones go in ebay fro $150 all the time. I bought one on ebay last month for $150 and it is fine. With that diagnotic tool, you can start turning away on that mixture screw. My CIS car runs best with the idle mixture at 3% though that would fail most states' smog test. You can set it at less than 1% for the test, then turn it back to 3%.

Is there a brand/model number to look for?

A pic might be cool if not to hard.

Thanks!

[76911S]

In addition, what search should I use on E-bay?

Thanks much..

[Doug Steinel]

Go to Ebay Motors... then go to Tools.... search exhaust gas analyzer. Usually there are Gunston analyzer for sale.... sometimes Heathkit. Mine is KAL.

[stlrj]

There seems to be too much mixture paranoia on this board. That being said, you don't need a CO meter to set the CO. Just set it to make it run right or the way you want and you cannot hurt your engine. If you set it a bit too lean, it just won't run right as you try to drive off.

The most difficult part is remembering which way to turn the CO screw...clockwise is rich and counterclockwise is lean.

If you can remember that, you'll never need a CO meter to spoil your fun.

Cheers,

Joe Garcia
86 3.2
Redwood PCA since 1976

[Doug Steinel]

Joe, I think your technique would work for me because my car is exempt from smog tests. Don't you think it would be a challenge to me if it wasn't? I guess you could lean it our by 1/16 turn before the test and most likely pass. Then reset after the test. What do you do?

[76911S]

Hmmm, good point Joe. But half the fun is the tools....

[stlrj]

Doug,

Even if your car were not exempt as most 76 and later CIS are, very few are set within the lean legal limit but are tweeked a bit rich by the owners or their wrenches to make them happy.

Happy tweeking,

Joe

[Hladun]

The comments here concerning tuning make me shake my head. You own a Porsche for God’s sake, if you’re going to tune it why won’t you spend $200 on the right tool (a CO analyzer). Every time this comes up (and it will here again I’m sure) a bunch of guys will come up with a dozen cockamamie ways of trying to set the richness. Yes I know that the engines run best at 3% CO, so set it there. But to all the smart guys, the people that are asking the questions here can’t tune it by smell (and I’m not kidding. On a previous post I said that in sarcasm and a bunch of guys seriously debated tuning by smell.) Spend a few bucks, get the analyzer, and do it right once.

[Doug Steinel]

And Ebay right now has 2 inexpensive exhaust gas analyzer listed right now.