mixture control

[hipdoc]

Anyone know where the air mixture screw and what size Allen is needed for my 1979 Porsche 930? It's running alittle lean. Thanks, Alan

[RarlyL8]

See that little post standing by the red air cleaner assembly?
I believe it is a 6mm allen head.
Don't force it down too far and don't adjust with the engine running. Turn from rich to lean a tweek after each adjustment.
I assume you have a Gunson or LM-1 type device to measure AFRs.
This adjustment only works for the idle mixture.

[rsrmike]

I thought it was a 3mm? why not adjust while running? just curious. I usually adjust w/ airfilter off, engine running. If it's lean, you can push the sensor plate down ever so slightly to richen it up and you will notice a change. If it's too rich, pushing down will make it run worse or stall. I'm talking not enough movement to really even see, visually. It doesn't take much.

That screw mostly affects the idle and very light load mixture, if you are lean across the board, you may have other issues

[Helmsy]

What afr should you aim for for warm/hot idle?

I presume adjusting the idle screw after mixture adjustment will effectively allow more or less air through and change afr's?

What are your procedures for adjusting mixture and idle?

[les_garten]

Heh, Well I think it is 4mm.

[356-930]

Originally Posted by Helmsy

What afr should you aim for for warm/hot idle?

I presume adjusting the idle screw after mixture adjustment will effectively allow more or less air through and change afr's?

What are your procedures for adjusting mixture and idle?

1) Both the sealing screw and adjusting screw are 3mm
2) Yes, adjust while warm, running
3) Turning mixture screw CW=rich, CCW=lean (Just a few degrees makes a big change - go easy)
4) Adjust AFR for 14.7 +0/-.2 (cover sealing screw hole with something like black tape during adjusting dance - the hole is a major air leak)
5) Blip throttle to reset arm on which screw acts before checking idle
6) It may be necessary to reset both idle air and mixture air to get idle AFR's correct. If so, it's dance back and forth to get it right.
7) Adjusting the mixture screw sets start point of the fuel head piston/sensor plate arm and thus the amount of fuel being fed to engine. Thus, AFR from idle through WOT is affected by this screw's adjustment. Important to get idle air/fuel mixture right then Control Pressure to get higher rpm/load AFR's right.
8) Don't forget to replace sealing screw before re-installing air cleaner assy.

[WERK I]

Originally Posted by hipdoc

Anyone know where the air mixture screw and what size Allen is needed for my 1979 Porsche 930? It's running alittle lean. Thanks, Alan

If you are running a little lean, then one click clockwise (right to richen, left to lean) should do it. You can do it while you're running at idle....just do not press down too hard. Very slight pressure down while you're rotating the allen to get it to slip into the socket.
Has this car been running lean since you had the car? Have you made any changes to the engine? Generally, this is a set once, forget about it adjustment. Header, cams, turbo changes, for instance, require adjustments. I always recommend checking hot and cold control pressures before touching that allen.

[A930Rocket]

What ever it is, I got tired of looking for it and JB Welded an allen wrench in there.

Quick easy adjustments now.

[9dreizig]

Originally Posted by 356-930

1) Both the sealing screw and adjusting screw are 3mm
2) Yes, adjust while warm, running
3) Turning mixture screw CW=rich, CCW=lean (Just a few degrees makes a big change - go easy)
4) Adjust AFR for 14.7 +0/-.2 (cover sealing screw hole with something like black tape during adjusting dance - the hole is a major air leak)
5) Blip throttle to reset arm on which screw acts before checking idle
6) It may be necessary to reset both idle air and mixture air to get idle AFR's correct. If so, it's dance back and forth to get it right.
7) Adjusting the mixture screw sets start point of the fuel head piston/sensor plate arm and thus the amount of fuel being fed to engine. Thus, AFR from idle through WOT is affected by this screw's adjustment. Important to get idle air/fuel mixture right then Control Pressure to get higher rpm/load AFR's right.
8) Don't forget to replace sealing screw before re-installing air cleaner assy.

356, what are the "sealing screws" you are refering to ?

[mark houghton]

Originally Posted by A930Rocket

What ever it is, I got tired of looking for it and JB Welded an allen wrench in there.

Quick easy adjustments now.

Ditto that...

[rsrmike]

Originally Posted by 9dreizig

356, what are the "sealing screws" you are refering to ?

The earlier 3.0 turbos didn't have the clever little spring loaded adjuster. They simply had a 3mm plug that exposed the actual adjuster on the AFM arm.

I think that's what he meant. And, yes, with those, the plug w/ affect the mixture for sure. I usually stuck my finger over them to seal temporarily...

[RarlyL8]

Yes, 6mm may be for something else, couldn't remember the size off the top.
I stated the general caveates as mentioned in the service manual. If you have never done that procedure before (and the question indicates this) then it is good to get a feel for the adjustment with the engine off so you do not damage the assembly.
It is typical for CIS to run more lean at idle in the wintertime if you have 4 seasons. If you want your mixture perfect all of the time you adjust it 2 times a year, summer and winter.

[Akila]

There are some helpful hints on tuning by ear. Most important one for me was, RPM will drop below idle point & then return to idle when rich. I have no AFR gauge, & may have just so happened to stumble on it, but mine is running smoooth!

[356-930]

Originally Posted by 9dreizig

356, what are the "sealing screws" you are referring to ?

The 3mm access screw that lets one get to the 3mm fuel mixture screw should have a copper sealing washer on it. When the screw is out, some of the air that is supposed to flow past the sensor plate flows instead through the screw hole. Basically, when the screw is out, a giant air leak exists.

[gogomobil]

Originally Posted by RarlyL8

It is typical for CIS to run more lean at idle in the wintertime if you have 4 seasons. If you want your mixture perfect all of the time you adjust it 2 times a year, summer and winter.

Thats what I found out a couple of days ago.
My AFR setting for summer at idle is 14,0.
Now as it was getting colder AFR shows 14,7 at idle.
Need to readjust for winter, but just a little bit.

[hipdoc]

I did some modifications on the car - K2700 turbo, 1 bar spring, MSD ignition, and GHL exhaust. After I start the car, it will RPM high during warm up but then ossilate between 200-1000 RPMs for about 6 times before idling at 900. It idles fine and runs good but I was told that it's lean and that's why it ossilates. I'm not familiar with a AFR nor how to use it. Please "school" me on how to adjust it correctly. Thanks, Alan

[9dreizig]

Hip,
The first thing you'll need is a LM-1 or LM-2 ( air/fuel meter),, with a way to hook up to an O2 sensor.. since you're in Fresno my guess is you're still running a CAT on your car ? If so you'll need to get either a bypass exhaust or install the O2 between the CAT and the turbo..
If you can do that I'll be happy to stop in sometime with my LM-2 and help you out..

[356-930]

Originally Posted by hipdoc

. . .After I start the car, it will RPM high during warm up but then ossilate between 200-1000 RPMs for about 6 times before idling at 900. It idles fine and runs good but I was told that it's lean and that's why it ossilates.

What you describe is an initial rich condition, not lean. Too rich, which is what's needed when cold, produces the hunting/oscillation at idle. Until the WUR is truly warm, it will hold control pressure low which creates a rich fuel mixture. (AFR = Air Fuel Ratio).
Until you instrument (shove an O2 sensor up the exhaust pipe and read it) you can't adjust AFR's closely. And, if vehicle is equipped with a catalytic converter, this may throw off reading of AFR's, I don't know about the new world.
You can adjust AFR at idle to get it close without instrumentation.
Get the engine idling with air cleaner off/sensor plate exposed. Press down on an edge of the sensor plate just enough to Barely move it. If engine speed picks up, too rich. If it stumbles/slows, OK to lean. If no change, you're spot on or close to it.
Best get an AFR system, Innovate or Zeitronix or? Zeitronix about $700 with all the sensors. I installed the Zeitronix and related sensors on my 930 engine because it logs AFR, RPM, Boost, EGT and throttle position simultaneously. A seat of the pants - street dyno (if you know where you can safelly accelerate through at least 3rd gear without getting a cop's attention).

[x98boardwell]

Hello,

I am also located in Fresno along with a couple other 930 owners. How long have you had the car?

Feel free to PM me your contact info. We all get together from time to time to help each other out and just recently dropped a fellow 930 owners car this past weekend in Fresno.

Look forward to hearing from you. Hope you get the system figured out.

Bryan

[x98boardwell]

We dropped his motor, not his car. Didn't want to scare anyone. Can't believe I didn't catch that sooner.

Bryan