Inherited '80 911 SC Targa-- Can someone please explain this CIS/Carb stuff to me?

[vash]

i got a stored 75 car started. if i can, so can you.

was it easy? no! was it kinda expensive? yes!! but to be honest, both situations would have been better if i cracked opened a book or two. there is a great CIS book out there..there are two actually. one is easier to understand, and there are pictures!! get that one. i have it in my garage if you want a pic of the cover.

AND..i think it would help if you posted up your location. you would be surprised who would show up to help..all for a beer and a slice of pizza.

pull the tank sender and take a peek..if there is little to no rust..you would be leaps ahead of the hot mess i inherited. and find CIS gauges. dont buy expensive ones..i did, and they look EXACTLY like inexpensive ones.

[nicfranc]

CIS for Dummies is a good place to start.

I knew absolutely nothing about CIS and got my 1980sc all sorted out with the help of this Forum. (also purchase Wayne's Book & the Bentley Book)

You can do it and it does not have to cost a lot of money.
My car has 300,000 miles on it and it now runs perfectly after I followed the sage advice of the Pelicans who were very generous with they time and knowledge.

You are in good hands and you have a great car.

[Tidybuoy]

I'm surprised that no one has mentioned the CIS Primer site (aka Jim's Garage). it really has a wealth of info and the specifications that you need to have a properly running CIS car.
911 CIS Primer - Index

There is a good chance that you will ultimately learn the hard was as most of us have been this route. I personally spent 2 years making my CIS progressively worse by tweaking things. Only to discover that once I had my fuel pressures set correctly, everything else started working.

CIS is really a very simple system but takes a while to grasp. it's basis of operation starts with proper fuel pressures. The correct fuel pressures will control how the fuel piston moves by using fuel pressure to dampen a small piston. Too much fuel pressure and the piston is hard to move and too little fuel pressure and the piston moves too freely. In either case, it's impossible to regulate the air/fuel ratio. Fuel pressures also vary depending on engine temp so there is a device that controls this (WUR).

You will have to read up on how all these things work together but the most important concept with CIS is to realize there is an order of operations. Certain things must be set first before adjusting the next and the key is to get the correct fuel pressure first. This is done with a relatively inexpensive tester that measures the fuel pressures at different operating situations. 1) system pressure = fuel pump main pressure. It is set to a constant rate of around 5 bar by a regulator spring within the fuel distributor and shims. 2) cold pressure = cold control pressure = fuel pressure out of the WUR before the WUR has heated up and 3) warm control pressure = fuel pressure out of the WUR after it has heated up.

The cold and warm pressures affect how much fuel pressure is applied against a piston in the fuel distributor. You might think of this as a nozzle on the end of a hose. The WUR uses springs and a metal disk to make it either easy or difficult for fuel to flow against the piston. Once those two pressures are set correctly, you fine tune the mixture and the engine will run fine for a very long time. Later versions, such as your '80 SC have added components that affect air flow. Most of these added devices are for cold starting assistance and once the engine is well warmed up, most of these devices don't do anything.

Bosch makes a very simple book on understanding CIS that explains the system well and the CIS Primer site is another great source of info. Lastly, I learned a whole lot from this board as there are some true experts here (I'm not one yet but getting there).

[Ronnie's.930]

The following old-school, K-Jetronic/CIS video is also worth a look-see.

Bosch K-Jetronic (CIS) explained - YouTube

[Bill Douglas]

Phew Ronnie. I'm pleased there wasn't an exam at the end of that youtube.

[wolds]

Excellent video, makes me feel smarter with that British accented narrator. If you understand this video you understand how CIS works. It's a simple system and works well if properly maintained and correctly set up. Warren

[82 SC]

Thanks Ronnie for the video, many this really helps

[Laneco]

When you drain your fuel, replace the filter/screen inside of the tank. This keeps the truly big stuff from going into your pump, but it tends to plug up with time (and especially after sitting). I consider it an "odd ball maintenance item" every 20 or so years on these cars.

Had a friend who fired up one that had sat for a few years. He went through three fuel pumps, which are rather expensive, before I convinced him to replace that part (host sells the part). Car ran like a clock thereafter.

This is the part # from our host: 911-201-141-00-M100

Just one more item to add to your pre-startup list.

angela

[david05111]

The replies to this thread have been fantastic. Thank you all!

The youtube video really helped me understand the system. It's simple on its face, but complicated in its nuances from what it seems. I totally understand the importance of the fuel pressure after watching the video. And I can also see why they abandoned this ultimately and went to EFI...there are just too many moving parts/failure points from my point of view. I mean, if for instance, one of the springs in the valves goes out of spec, it could affect every component down the line.

I'll read up on the system some more on Jim's site to make sure I understand it.

Apologies again for the delayed responses. I'm posting this at 2:04 eastern time, but I'm guessing this one too will require moderator approval, which slows down the true post time.

Anyone have that information on the K40 filter from my last post? (Bottom of page 1).

[Porsche 2]

TidyBuoy, great summary explanation. Thanks.

[targa80]

David,

Congrats on getting the car.

In reference to the CSI vs. carb discussion, my suggestion would be if the car has not been messed with and the K-Jetronic with Lambda CIS system is complete, then stay with it. When it is fully functional it works as designed and granted you will need to learn how the system functions under the different operating conditions. I agree with all of the previous recommendations on reading material and also I would recommend the Bosch Fuel injection manual. It has a lot of technical info on the design that I found to be very helpful in understanding the system.

Pat

[lonewolf]

+1 on Jims CIS primer.

[david05111]

I just thought I'd add an addition to the thread about service records. I have some, but my father has never been (nor ever was) a great collector of them. So I've only got a few of them, but I do have the original Owner's Manual and Warranty and Maintenance Manual. Unfortunately, I do not have the original window sticker or receipt of purchase (other than a sheet which certified the mileage at the time of transfer).

[euro911sc]

Too bad you are too far north or I'd stop over and give you a hand.

[david05111]

Originally Posted by euro911sc

Too bad you are too far north or I'd stop over and give you a hand.

Haha thanks for the offer man! I've got quite a bit to do with her before I attempt a start so I'm not too convinced I'll need outside help...yet

[sfjyying]

YA, what he said!

[david05111]

Going through the car tonight guys...my parts came in.

I need to know what a good oil to fill her up with is. I'm in Florida, so it's hot and humid. Thoughts?

[Lusso1]

any oil that is 20W-40, you will run it 100 miles then drain it and repeat for 500 miles

after that, switch to Brad Penn

[david05111]

Cool, thanks for the input.

Next question. The plugs I've been pulling out of the engine are old Bosch W6s.

The ones I ordered from our sponsor are Bosch WR-5-DC+S. Are these compatible? They say they are when ordering, but it admit that I didn't look at the ones that came out of the engine until I had replaced 3 of them.

[HarryD]

Nice car.

Do not let the CIS naysayers poison your thoughts. If what you want is a nice car to drive every day, CIS is hard to beat. If you want the last 1/10% if it's performance, Then by all means go to carbs or EFI. For what you will spend to convert , you will have paid several times for the CIS rehabilitation. You will find CIS easy to start (carbs can be finicky on a 911), good mileage and very robust. I have had my 1973.5 (world first production car with CIS) for over 10 years and it had not needed anything other than a minor adjustment 9 years ago.

Keep what you got and educate yourself or find a mechanic who knows how to
maintain a CIS system.