How do I set the mixture properly on my 911 CIS (non lambda)motor?

[Daviboy]

Guys,
I know I am going to take a lot of flak here so am hunkering down for the barrage. I have an 82 SC without lambda sensor as I have headers and no O2 sensor. Everywhere I read (here and Rennlist forum) all the advice for setting the mixture on the motor is for cars with lambda.
I think I basically understand the CIS system however how do I set mixture after an air-box replacement?

[Joe Bob]

Best is to make sure your fuel pressure is good, get the long hex key and use a smog box for the tail pipe.

[T77911S]

i set mine by making small CW changes until it surged at idle, then turned it CCW about half a turn then CW to the last place it did not surge. drove it and if the RPM's dipped down when i let off the gas, then i would do the CCW then CW and make it just a Little leaner until the RPM's dont dip. i had it checked later and it was dead on 3%. basically, set it as rich as you can without idling problems.

[john walker's workshop]

find a shop with an exhaust analyzer and set it to 3-3.5%.

[Daviboy]

Thats it stick an O2 sensor in the tail pipe and adjust idle mixture till 3-3.5% reading achieved?

[Kemo]

Originally Posted by Daviboy

Thats it stick an O2 sensor in the tail pipe and adjust idle mixture till 3-3.5% reading achieved?

Yep thats it...I took John Walker's advice on this many years ago. Back then he also recommended a timing setting of 5 degrees BTDC. JW is one of the real guru's on the board, we are all glad to have him as a resource, IMHO.

Also know that as you adjust the CIS mixture you will change the idle RPM. Changing the timing will alter the idle as well. So, I set my timing first, then adjust the CIS keeping the idle around 1000 RPMs. After getting the A/F the way you want it, dial down the idle to 950 or so... At least that the technique that works for me.

[Daviboy]

Kemo,
Thanks just cannot believe it is that easy, this I will attack on my own no problemo. Excuse my ignorance but what does BTDC mean....doh my guess is Before Top Dead Center, am I correct am I am I? If so how is that done??? Sorry

[snbush67]

Correct on the BTDC. To set it you need a timing light and adjust your distributor by loosen the mounting nut and rotate it slightly to set it at 5 deg, btdc at 950 -1000 rpm.

[Gunter]

Originally Posted by Daviboy

Guys,
I know I am going to take a lot of flak here so am hunkering down for the barrage. I have an 82 SC without lambda sensor as I have headers and no O2 sensor. Everywhere I read (here and Rennlist forum) all the advice for setting the mixture on the motor is for cars with lambda.
I think I basically understand the CIS system however how do I set mixture after an air-box replacement?

Even though you don't have a sensor, the rest is still Lambda unless you removed other components?

Set the mixture as advised by others; it takes a few tries between mixture screw and the fast-idle screw.

Set the timing at 5 deg BTDC with vacuum disconnected at ~950 RPM.

[Scott R]

If its still has the lambda gear and no O2 sensor you need to get it sorted. If you search under my name you will see two dyno runs, one with the O2 sensor hooked up and the mix set per the factory. The second is disconnected and set to 3.5%, the 3.5% run is a mess, AFR's are all over the place and power is down.

With the sensor connected and all of the equipment working the AFR's are near perfect and the power is much better. The default operating mode of the frequency valve appears to cause this.

[boyt911sc]

Originally Posted by Gunter

Even though you don't have a sensor, the rest is still Lambda unless you removed other components?

Set the mixture as advised by others; it takes a few tries between mixture screw and the fast-idle screw.

Set the timing at 5 deg BTDC with vacuum disconnected at ~950 RPM.

Gunter,

Could you be more specific about what other component/s needed to be removed? And why? Thanks.

Tony

[Daviboy]

Originally Posted by Gunter

Even though you don't have a sensor, the rest is still Lambda unless you removed other components?

Set the mixture as advised by others; it takes a few tries between mixture screw and the fast-idle screw.

Set the timing at 5 deg BTDC with vacuum disconnected at ~950 RPM.

Even though you don't have a sensor, the rest is still Lambda unless you removed other components?

Gunter mine is a euro ROW model therefore no lambda equipment or sensor. I would appreciate a post with pics of setting timing if possible!

[Gunter]

Originally Posted by boyt911sc

Gunter,

Could you be more specific about what other component/s needed to be removed? And why? Thanks.

Tony

On a 1980-83 US 3.0 with Lambda, a lot of people use the CIS from 1978-79; it has larger intake runners and no Lambda.
No brain, no Frequency Valve but still has AAR, AAV, Decel.Valve, TTS, CSV.

[Kemo]

I dont have any pics...but a good thing to do would be to find the markings for setting the timing and make sure you can clearly see them before you hook up the timing light.

just to the right of the Z1 mark, you should see another tickmark, possibly with a 5. This is the 5 Deg mark and thats what you line up to the tick mark just above the wheel when you spin the distributor to adjust the timing. Some timing lights allow you to preset the light with a certain advance or retard. If you are using the 5 mark to line up, make sure your timing light isn't set up for advance.

I think now would be a good time to suggest Waynes 101 Projects book. It has great pictures for doing this. I also think some good pictures could be found searching the threads for valve adjustment, as you need to use the markings for this procedure to get the #1 cyl to TDC.

[Daviboy]

Kemo,
Thanks I have Waynes book coming in a shipment along with a new airbox + gaskets and ruubers, front rotors and pads + caliper rebuild kit, clutch cable, pedal bushing kit, headlight relay kit, factory short shift kit + new bushings, valve cover gaskets, oil filter + seals, and some other goodies. So I will be leafing through his book quite extensively in the weeks to come. I am sure the wife will be charmed but what the hell it keeps me out of trouble.... well other sorts of trouble lol.

[Kemo]

Originally Posted by Daviboy

I am sure the wife will be charmed but what the hell it keeps me out of trouble.... well other sorts of trouble lol.

nice...i agree.

let us know how things turn out with the projects and good luck.

[otto in norway]

Sorry if I'm intruding here...

What if you want to adjust the mixture without the cat installed? (I have a pre-muffler installed instead)

What will the correct O2 sensor reading be then?

Otto

[MBEngineering]

HI Daviboy
If you a 81/82 engine then you need to look at this chart, if it is NOT US spec, as the CO% will be to high at 3% and the engine will hunt at idle;



has your engine a air pump on the L/H side of the engine ne'er the dist, if so remove the belt before adjusting the CO%, and always adjust the CO% from weak to rich as the small relay arm in the air flow sensor plate will be tight and some times sticks.

regards mike

[holtjv]

Oh and if you buy the pelican "T" allenhead tool for adjusting the mixture you'll probably have to cut down a bit--too high for my 79, anyway. Or find another allenhead.

Good luck and have fun with Wayne's book--should pick up a Bentley, too. Between the Board, Bentley, and 101 you ought to be able to figure anything out.

[Daviboy]

Originally Posted by MBEngineering

HI Daviboy
If you a 81/82 engine then you need to look at this chart, if it is NOT US spec, as the CO% will be to high at 3% and the engine will hunt at idle;



has your engine a air pump on the L/H side of the engine ne'er the dist, if so remove the belt before adjusting the CO%, and always adjust the CO% from weak to rich as the small relay arm in the air flow sensor plate will be tight and some times sticks.

regards mike

Mike,
My car is non US it a ZZZ ROW car. Is there any way you can scan and send me that chart, it is ompossible to read from the picture? If so send to davy_1010@yahoo.com