CIS to Carb HELP!

[Jay Laifman]

After spending lots of money to rebuild my 73.5 CIS T engine to spec, including new P&C, rebuilt CIS heads, lots of new CIS components, it looks like the smallest of parts maybe the giant killer: the throttle position control regulator. It looks like mine is bad and it is simply NLA. I will certainly spend lots of time trying to find one. But I need to start considering the reality and options.

Had I known this was going to happen, I never would have done the CIS domed pistons or CIS heads, and I would have gone a completely different direction before the rebuilding the engine. I'm not inclined to junk all that stuff.

So, from those of you who have done it, what I want to know is if I leave everything CIS specific, that is pistons, heads and cams (cams that were specifically detuned for the efficiency of the CIS), and simply put on Webers or PMOs, will it be remotely a decent car? Note, I do in fact like the smoothness, long torque curve and reliability or CIS. Or, do I need to change the heads and cams to get it to be a sports car again?

I guess the worse it is, the more I'll try to find the regulator or the more I'll investigate getting different heads, cam, carbs.

(Of course, I'd also welcome someone having a lead on the regulator).

Thanks.

[RoninLB]

fwiw

I rebuilt with forged RS pistons and reused the stock CIS FI and cams till I had more $ for new cams and carbs.

CIS FI & RS pistons ran great together.

[Jay Laifman]

Originally posted by Noah
Just post a WTB ad on the parts classifieds, and call the various Porsche dismantlers. I don't see the sense in spending $2-$3K on carbs when all you need is a $40 (or whatever it costs) part.

Remember: learning how to suppress your frustration is one of the great benefits of this highly irrational old-car hobby.

Thanks. But, what I'm told is NLA is NLA, that there are no new ones and no rebuilt ones and no way to rebuild them. These were only used for a couple of years, if even that. And, even if I find a CIS system sitting somewhere, chances are that the internals of the regulator are shot from age and non-use. That said, I agree with you completely. My goal is to find a working one. But, as my desperation grows, I was hoping to know my alternative to gauge how hard I should continue to search before I give up.

[JP911]

If you can't find one, there may be a fix that allows the CIS to function without it. From all of my studies/work on my CIS I've found that the only truly essential external (excluding the obvious like the airbox, fuel dis, etc) component of the system is the warmup regulator. Of course, I ended up throwing in the towel and going to PMOs.

[Jay Laifman]

Ok, Jon, so to my first question, did you only put on PMOs and leave the CIS heads and cams, and if so, did you like the results? Or did you make other changes to benefit from the PMOs?

[azasadny]

Jay,
Post a pic of the part you need. I have two "almost complete" CIS setups from my '74 and they were on the engine last summer before I converted to Webers. I'd like to help you if I can...

[HarryD]

Jay,

Bosch K-jetronic was used on many makes in the '70s and '80s. Saab, Audi, MB, VW, Volvo, to name a few. Try looking for k-jetronic parts and don't worry about the Porsche name until you get closer to finding what you need. I presume you have spent some time at the your local "oldtimer" shops to see what they can do to help you.

[JP911]

Jay-
My situation is kind of apples-to-oranges as my motor was far from stock to begin with (3.5 built from a 3.0 and I tried to run CIS but it was too choked down). Now, as to the question as to whether or not you can run carbs with CIS pistons and cams, the answer is "yes". Many people make this upgrade. Could you get more out of the motor with different pistons and hotter cams? Yes. But you're car will be streetable and will likely have better throttle response with carbs. But, I'm not saying you should run out and do it. I think your CIS problem can be solved.

[Jay Laifman]

Wow! Here you go, it's number 28 on the side of the throttle body:

[azasadny]

Jay,
I seem to remember that on my car, this device was not connected at all. If I can remove it from the rest of the CIS, I'll send it to you. PM me with your address.

[EarlySport]

I switched my 1980 911SC motor from CIS ( Crap Injection System right? :-) ) to 40mm Webers.

I made no internal changes to the motor. I also backdated the exhaust.

I love the way my motor runs. No problems starting, great throttle response, and seems to pull harder at the top end. I get no flat spots or drive-ability issues.

I ordered a complete set of venturi's and jets from PMO - their recommendations. The car hasn't been dynoed.

I also love the way the motor looks, and I think troubleshooting potential problems is much easier.

Where I live we don't have smog testing - that may be an issue for you.

Craig H

[HarryD]

Jay,

Looking at my PET, all CIS cars up to '77 had this device and then it disappeared.

[Cipotifoso]

From what I've found out, this device was phased out sometime during the mid-'75 model year. My (very late) '75 has the shaft on the thottle body to which this device would mount, but no device. From the documentation I've read, this is how it came from the factory.
If the part cannot be obtained, one option would be to update other parts (WUR) to match a later configuration where this part was not used.

[Jay Laifman]

Thanks for all the suggestions and help. Right now I'm anxiously awaiting Art's regulator an hoping it will solve everything (you know, "everything" = the meaning of life, the universe and everything). Short of that, I'll be happy if saves my car and makes it run the way it's supposed to. Thanks again Art!

As to retro fitting later CIS parts, the problem is that the later cars did away with the Throttle Position Regulator by adding a vacuum line ported from the distributor or intake. My parts don't have that vacuum. So, I'd have to swap in the part with the vacuum. But, that part would not be designed for a 2.4, but a 2.7 or 3.0. Then I'm stepping into crazy unknown territory. I've yet to find anyone who has successfully done such changes. I think the jump to carbs come pretty quickly at that point.

[azasadny]

Jay,
I'm out here in my garage right now fighting with this thing. I've removed the two bolts that hold the device to the throttle body but it still won't budge. What's the secret to removing this part without damaging it? Both of my CIS setups have this part but the fuel line was disconnected on both of them... Sorry for the delay!

[Jay Laifman]

Ah, it needs to slide off the shaft away from the throttle body. You may need to take off the bolts holding down the throttle body to lift it enough for the part to slide laterally enough and not hit the other side.

[azasadny]

Jay,
I just got home and I'm in the garage, I'll try again. Thanks for the tips!

[azasadny]

Jay,
I'm sending you the throttle body with the throttle pressure control valve attached. It will go out this afternoon. Good luck!

[azasadny]

Jay,
I sent you the control pressure regulator with the fuel line/banjo fitting attached, the other one I have has a cut-off fuel line. Neither one was attached to anything...

[Jay Laifman]