What comes first , idle or mixture
 

Do you guys try to set idle to 950 rpm then even out with mixture? (good warm engine)

When I even out with mixture the idle increase then turn down the idel even out with mixture then down with idle..... how far do you go before I hit bottom out.

On some old carbs the rule of thumb was something like for a starting point. ( turn idle screw all the way in then back it out 1 1/2 turns for starting point) is there such a rule of thumb on a CIS?

thanks
Willie

The rule of thumb I've always seen on these boards is "don't touch the mixture until you've thoroughly eliminated air leaks and ignition issues including O2 sensor / lambda, and set the timing properly" so I would guess most folks on here are going to say set idle speed with the air bypass control screw, then time the car, then set idle speed again, then time again, then dial in the mix...or something like that ;)

Thanks Jason

Forgot all about setting the timing also, makes sense. New O2 sensor. Rechecked again today for leaks.
Zimmerman had a nice paragraph that I found as well.
Thanks again
Willie

Ok found my old timing light. ... Last time I used it was 71 or 72... bulb burned out... off to the parts store an of coarse they don't make anything like that anymore :) This is where you guys are gonna laugh at this old man.... the new Bosch does all kinds of neat stuff... one of which reads the RPM right on the timing light!!!!! o.k. you can stop laughing now, I'll get there.
Anyway...
Warmed up engine
set idle to 925 + or - 50
take off both vac lines on dist.
re-set idle to 925 = or - 50
set timing 5 BTDC

lock down dist
both vac lines on
re-set idle
re check timing

set mixture

it will still fluctuate about 20-25 rpms is this a good spot (950-975) ? Is it suppose to be better?

Thanks
Willie

how are you setting the mixture?

usually a surge means rich, that's not much of a surge. for one that small I would have to hear it to be sure.

You mentioned new O2 sensor, so I presume the Lambda system is active. From what I understand, that is going to induce a slight oscillation in idle as the controller hunts back and forth in response to the narrow band O2 sensor output around stoichiometric.

Thanks guys.
Makes sense on the O2 sensor, good point Steve.

T77 I did make a small mistake of leaving the small Allen wrench on the mixture arm while adjusting idle. That little bit of weight still makes difference. Adjusting 1 click at a time then remove seemed to make it much better. The timing was off about 10 degrees as well which made a big difference.

In the airplane world we have an adjustable "Vernier" cable so we can "lean to peak" but it will burn hotter. Is that a concern here on this or if it gets too lean it just doesn't run well?

Thanks

10 degrees is a lot. when I find something way off I make sure I am doing things right. you may want to double check. I take

with the lambda you HAVE to set it to spec and do it how the manual says to do it.

if you bypass the O2 it likes to run richer more than lean,.

There's a CIS subculture of people on Pelican (Jim Williams, psalt, Bob Kontak, et al) very knowledgeable about the Lambda system. Here are some of my bookmarks:

http://forums.pelicanparts.com/porsche-911-technical-forum/598223-unplugging-o2-late-scs-fuel-enrichment-question.html

http://forums.pelicanparts.com/porsche-911-technical-forum/513312-cis-idle-question-open-loop-behavior.html

http://forums.pelicanparts.com/porsche-911-technical-forum/544758-help-odd-02-frequency-valve-behaviour.html

In a nutshell, when in closed loop (engine warm, not at WOT) Lambda can adjust mixture within a limited range. Setting the 3mm screw on the fuel distributor gets the Lambda "centered" so it can trim both leaner and richer as needed. This is slightly different than the adjustment you would make on the 3mm screw for a CIS Basic (no Lambda) system.

LIke T77911S says, there is a specific procedure to adjust the system. If you have an old fashioned dwell meter (or an oscilloscope) to observe the frequency valve duty cycle (this is what actually affects the mixture) you can adjust the 3mm screw so the frequency valve is operating at mid-range.

I run a wide band O2 sensor on my track car ('82 motor). It outputs an emulated narrow band signal that is routed to the Lambda O2 sensor input. People have had mixed results doing this, but it worked for my AFR meter. I noticed a slight "hunt" at idle, but the AFR is fine at WOT (important for a track car) and my plugs have never looked better, despite running a fairly cold plug.

Turn the big air bypass screw in all the way until it bottoms. The car should stall or barely run at 200 RPM. This means air leaks are reduced to a minimum.

If it runs at 600 RPM you are sucking air.

T77
I have changed a lot of other stuff in the last 2 months. New injectors new wires new rotor cap an rotor etc etc. My guess is over the years to compensate other issues the mixture an timing have been adjusted. So everything no is back to acceptable limitts stated in the Bently.

Had the car out again this afternoon. Wanted to start it up cold again. All good with in 3-5 min. I was coming off high idle. Settled in at 955 to 980 rpms. Took it out for a 1/2 hour spin. checked rpms remained the same. Ran very good.
Maybe I'm just not use to the CIS an the lambda an O2 sensor allowing the rpm to fluctuate a bit.
I will try an see if one of my buddies has a gas meter to measure the exhaust. Can't really tell weather I'm a bit rich or a bit lean.
Fun stuff though always more to learn :)

I never checked the RPM fluctuations on the tach but you can open the engine lid and hear it switching at idle with the Lambda functioning. Not a switch noise but a tiny difference in how the engine runs every few seconds.

Try to get the CO dialed in. Downside is if baseline (without Lambda) is too lean, you leave a little power on the table at WOT.

Good work!

Thanks, will update later

Willie, I would set your timing at 4000 rpm. And correct timing depends on other things like fuel qaulity and comp. Every engine is a little different. I would start off at around 30 degrees at a steady 4000 rpm and go from there. You have 9.3 to 1 comp. in your 83 sc, with 93 octane I run around 36 degrees full advance, but I have 9.8 to 1. Let the idle fall where it may, thats not what your looking for. You want max. adv. that your engine can deal with. Sounds like you are on the right track, you will hear the engine idle flux a little when the lamda is working properly.

When the lambda system is running right it's supposed to fluctuate very slightly - you can see it on the tach - just very slightly wavering.

Ok
31 at 4,000 rpms. Did notice an improvement with a smoother acceleration in the power curve. The lower end of the power curve was just a be sluggish but better response on throttle today.

Man this is really great, thanks everyone..... I'd better be carefully or Johnny Law will be asking me for a donation :) :)

I have 1 more big task at hand..... Valve adjustment. I have not done this yet and really don't know when it was done last so hope to capture a bit more HP when that is done.

I think I'm just going to drive it the way it is now for 2-3 weeks before I start on that, I'm having too much fun :)

Go to 2500 rpm in 3rd, slowly floor and listen for spark knock with windows up. If no knock, keep advancing until you can hear it, then back off just a tad. They are all pretty sluggish until around 3500 rpm. If sluggish after that, might need to check control press. to make sure your not to rich. Valve adj. no big deal. 4mm is pretty easy to gauge by feel. If the gap feels good, leave it alone. Main ones you are looking for are ones that are to tight

The SC maxes out at sub 3,000.

You are 8-9 degrees past max timing at 31.

You sure you know what you are doing?

Sorry to be a killjoy.