Love that CIS

[Paulporsche]

Went out this morning for a drive. It was 2C (35F). I got a couple of pops of the old popoff valve, so I gave the mixture control unit a 1/8 clockwise turn and it's back to smooth running.

This will probably do me until I put the car away in about 5 wks.
Come next spring I can gradually lean it as we get back to warmer temps.

Since I have no O2 sensor, DME, or other electronics to do this for me, what could be easier?

[Brother]

how many years have you been doing this.

It has been that cold for weeks now. I might give it a try.

[cantdrv55]

Paul, the mixture adjustment is a mystery to me. I can't seem to get it right as I'm either turning it too much or going in the wrong direction. When my CIS needs adjustment, I pay to have it done right. I'd love to save the cash. Please help me understand why you turned it CW (I guess to richen?) when the outside temp is low.

[Brother]

I would think it is because cold air is more dense and therefore is enviromentally leaning your mixture. Hot air would do the oposite.

All the jets I've flown have been completely different in the performance area depending on whether it was cold or hot outside.

[cantdrv55]

Originally posted by Brother
I would think it is because cold air is more dense and therefore is enviromentally leaning your mixture. Hot air would do the oposite.

All the jets I've flown have been completely different in the performance area depending on whether it was cold or hot outside.

Does dense cold air = more oxygen which means you'd have to increase fuel flow to equilibrate the mixture?

[larry@oma]

mixture adjustment on a 78 sc? turn clockwise to richer? where is this adjustment ?

[OldTee]

Right-ie Rich-ie; Lefty Leanie. and ever so slow. Keep a record.

[Brother]

Originally posted by larry@oma
mixture adjustment on a 78 sc? turn clockwise to richer? where is this adjustment ?

Between the fuel control and the big pineapple looking thing on the very top of your engine there is this inconspicuous hole or a plug in a hole. You can put either a 3mm allen wrench through it or the CIS adjustment tool.

[Paulporsche]

Brother and Chris

You have the right idea. I have been doing this w/ my car for over 15 years/80,000 mi, and before that, for 13 w/ my old 78 Scirocco, and to a much lesser extent w/ my 85 1/2 944. Richer in the fall and leaner in the spring to compensate for the density of the air. Here in Toronto I'll be driving the car until about 15 Dec, at temps down to about 20-25F. When I pick it up next 15 Mar it will probably be about 25-30. As the spring progresses I'll start leaning.

Since the hottest summer temps here are usually a max of 90-95F, with high humidity, the leaner mix is fine. I have read some posts, especially those about engines w/ chips, that hotter engine and ambient temps can cause problems, but in my climate that's not the case. In fact I can get the symptom that some have mentioned whereby the revs want to drop radically when coming to a stop, during high temp/humidity conditions (say in August). Over the years I have learned this means a too rich mixture. Likewise I have observed that any popping of the popoff valve means I'm too lean.

Since I don't need to have this car checked for emissions, I don't know what my CO is. After reading numerous posts on this, I figure if I am set just shy of the fluctuating idle threshold (point of being too rich) I am @ about 3.5%. I am also guesstimating that one complete rev of the mixture screw is about 8%, so I usually limit my adjustments to 1/32 or 1/16 turn @ a time. I then drive the car and see what happens.

I am not a mechanic, and compared to many of the posters, do not even have the experience that quite a few do regarding DIY on their cars. I have, however, noticed that the car gives a lot of feedback regarding the mixture which is easy to read and use. For instance, aside from the above symptoms, I can also hear a too lean condition. W/ my Dansk/SSI setup I get a decidedly "growly" or raspy exhaust note when leaner. Richening gives a mellower tone.

Old Tee,

That seems like a good mantra, and if someone is new to this, keeping a record is probably a good idea.

Larry,

You should search this as there are many posts, incl pics, that will show you how to do this. I think there is info in Wayne's book too. Basically you find the small hole in the top of the mixture control unit between the fuel distributor and the rubber bellows. On later cars this may be plugged and need to be drilled out. If you are lucky you will still have a removable plug w/ a handle there that you can lift out. Put a 3mm allen wrench in there and do the adjustment. Don't push down when adjusting. If you can't fit the wrench in, the screwhead may be junked up. Take a piece of wire and clean it out. I have made a replacement plug from a piece of brass tube and some plastic shrink tape to keep dirt out of there. I do the adjustment w/ the engine off, although some like to do this while it's running, richen to the point where the revs drop, and then back it off just a little. Others have posted a technique in which they alternately raise and lower the sensor plate and see if the revs rise or fall to tell them if thet are set right. I guess you should do whatever works for you.

I would say that this is the same as w/ any DIY project. If you are not comfortable doing this yourself, have a pro do it. I have found over the years that I am much more sensitive to my car than any mechanic was on this, and can make these micro type adjustments w/ greater accuracy.

Let me know if this works for you.

[Superman]

I've been driving CIS cars for a lot of years now and when these systems are working properly, it's hard to imagine a smoother or more convenient system. Starts instantly, runs smoothly hot or cold, etc.

[Sunroof]

My 1973.5T CIS is the first system and lacks the thermotime switch and has a more primitive warm up regulator. I have a hand throttle opposite the heater handle between my seats. For start up I just lift the throttle up about one-half and she sparks off like magic! The only problem is, is that I change the throttle til warm up. This system has the feel of an older MG or Triumph.

Here is a heads up for those who might be having a problem adjusting the mixture screw...............

The previous owner either by his mechanic or his own hand placed "lock-tite" on the mixture screw to hold its setting. Nuts!!!!

When I first got the car, it felt like it was turning although you could not feel the classic "click". I was running lean, blew the pop-ff valve off the box, and could not figure out what was going on. It took a savy mechanic to realize what had happened and he picked out the stuff so that the allen wrench could makes it way in for the successful turn.

The CIS is a great system and has been very dependable for me, but I did replace just about everything including the WUR with a brand new original unit that was found covered with dust in some Stuttgard basement.

Regards
Bob

[larry@oma]

my 1978 sc cis is running fine.but realy good info to have.--thanks guys.--

[HarryD]

Paul,

After reading tons of posts on how you should get rid of that "pesky" CIS, I am glad to see that someone came out of the closet and admitted that for drivability and easy motoring, a properly setup CIS is tough to beat.

I too like how it behaves. Compared to my newer EFI cars, the backyard guy can actually do some work on the system to correct problems without a ton of fancy electronic gizmos. And as you note, the feedback is clear.

Just sign me another happy CIS guy.

[Brother]

I agree it works well and is fairly simplistic.

I would think about losing it for the cosmetic value as much as performance. It does have some performance problems compared to carbs or efi but not too much. FI in general is supposed to make life easier and less involved with the day to day tuning of the intake, but it has its compromises.

Mine isn't going anywhere unless the other options drop in price significantly, and I think the SSI and dual out muffler is probably higher on the list.