what should I do with my CIS? 4 options...

[WVU 911]

I have had my SC for over 3 years now and the cis system has never worked properly...it was missing the mixture screw when I got it. My mechanic has it now and hopefully it will be working properly after he is done. Im not going to do anything with it til after I get it back and something goes wrong, which hopefully wont be for awhile! Anyways, when something goes wrong I could either fix the cis, convert to PMO carbs, convert to EFI, or according to my mechanic I can find a complete motronic setup including the wiring harness, intake manifold, sensors and computer. I was wondering what you guess would do and why? Which option is the best. Once I decide what I am gonna do I need to research it more and find a place to get parts. I appreciate your responses, Thanks guys!

Geoff

[makaio]

Efi

[boyt911sc]

Originally Posted by WVU 911

I have had my SC for over 3 years now and the cis system has never worked properly...it was missing the mixture screw when I got it. My mechanic has it now and hopefully it will be working properly after he is done. Im not going to do anything with it til after I get it back and something goes wrong, which hopefully wont be for awhile! Anyways, when something goes wrong I could either fix the cis, convert to PMO carbs, convert to EFI, or according to my mechanic I can find a complete motronic setup including the wiring harness, intake manifold, sensors and computer. I was wondering what you guess would do and why? Which option is the best. Once I decide what I am gonna do I need to research it more and find a place to get parts. I appreciate your responses, Thanks guys!

Geoff

Geoff,

How on earth could you lose your the 3-mm air mixture screw!!!!!!!! The fact that you don't have one really put you in a bind. You would never have the correct air mixture in the first place. Are you a DIY type individual? If you are, then I might be able to help you. What year and model is your car? Got catalytic converter? Got a CIS fuel gauge kit available? Have a digital camera?

As a background, what was the major problem with the CIS engine? PM me if you wish and I'll be more than happy to assist another fellow 911 enthusiast. BTW, CIS is completely different than Motronic system. Keep us posted.

Tony

[RWebb]

Originally Posted by WVU 911

... Which option is the best[?]...

Like any optimization problem, you first need to define the constraints.

What are yours???

$$

emissions regs.

use of high EtOH levels in your area in future years

driving usage

a search on CIS + carbs + EFI and variants thereof will give you some useful backgnd. reading

[racer]

Given the age of the CIS system, it sounds like, ideally, it should be completely removed and overhauled by someone familiar with the system. Period. Replace all old corroded lines (fuel, vacumn etc). Make sure components like the wur are working properly etc. I have enjoyed my CIS 911 so much more than my previously owned carbed 914.

While of your replacement choices I choose carbs, they really won't be much fun unless you change out the mild CIS cams, so factor in that cost. Then there is the need to make sure they are set up properly at install. If you drive the car year round (extreme cold or heat) carbs can be a pain. They will also increase your fuel consumption. And, as mentioned, are there any emissions concerns to be met?


The fact that your mechanic wants to sell you something tells me he isn't perhaps as well versed in CIS as you need.. just saying.

[schumicat]

I would do a Megasquirt conversion.

[47silver]

Tony (who has helped me tremendously concerning CIS) and other members or this board will get you running properly.
CIS is a fairly simple system that has 2 sub-systems.
I consider it to have a WET side sub-system and a dry side sub-system.
The WET SIDE sub-system Components
fuel pump
warm up regulator.
fuel distributor, with air mixture air flow meter.
6-injectors and seals.
cold start valve
Thermo switch.
fuel pump switch on the fuel distributor (some dont have this)
supply and return lines.
Fuel injector lines.
Warm up regulator control line and supply line.

The DRY SIDE sub-system components: Remember this system works on a vacuum caused by the intake valve opening and the piston pulling a vacuum. It is imperative that you do not have any leaks.
Air box.
Throttle body.
Idle mixture screw.
6-Rubber manifold connectors.
on some there is an auxillary air device, some just use a manual lever.
Deceleration valve. (this is the only component that can be eliminated without degrading the operation)
6-maniford gaskets
6-Inject valve plastic sleeves
I may have left something out maybe a throttle switch?.

If you methodically check each of these components and bring them up to spec. you will have a very reliable easy to start and surprisingly economical engine.

On this board everyone of these items has been addressed.
I pulled off my cis without dropping the engine, it was not too difficult if you are a contortionist.

[James Brown]

Good one 47 silver, but it's also called the fuel leaking side and the vacuum leaking side.

[kwc98]

The nice thing about going EFI, is that you can actually work on the engine without a partial drop. It really cleans up the engine, gives you room to work and of course it gets rid of all of those crazy CIS hoses just waiting to leak. CIS seems to need alot of voodoo to make it work. EFI is actually sensible. I have the Tbitz (megasquirt) instead of CIS, a vast improvement.

[T77911S]

it depends what you want out of the car. do you like the sound, look and performance of carbs? do you want the performance and fuel economy of EFI, or do you want the reliabilty, fuel economy of CIS?

CIS is a VERY reliable system. if your car is pre 80, the only thing that will keep your car from running are the CD unit, coil and fuel pump. CIS is really not that hard to work on once you have a little understanding of what each part of it does. and if yo follow the advice here, you can work on it. CIS is also limited to cams. but a 964 or SC cam, depending on what car you have, will be a nice improvement.

carbs are awesome. they look great, they sound great, but,,,,they are harder to adjust, as opposed to CIS's one mixture screw.

EFI, more electronics to fail. i dont know much about this as far as what people are putting on their cars. but once setup, i would think it would be an awesome system for performance and fuel mileage.


it sounds like you will already have a lot invested in the CIS. depending on how good your wrench is and if he fixes all the problems may be the factor for which raod you go.

me? and money was not the issue, carbs. for the reason above. but then i can work on them and i am not worried about the mileage.

[azasadny]

I've been running Webers on my unmodified '74 with 2.7L engine since 12/06 with no problems. I drove the car 3600 miles in 6 days a few months after Tab Tanner rebuilt and installed them on my car and it's been smooth sailing ever since. Just my .02 worth...

[boyt911sc]

Originally Posted by kwc98

The nice thing about going EFI, is that you can actually work on the engine without a partial drop. It really cleans up the engine, gives you room to work and of course it gets rid of all of those crazy CIS hoses just waiting to leak. CIS seems to need alot of voodoo to make it work. EFI is actually sensible. I have the Tbitz (megasquirt) instead of CIS, a vast improvement.

kwc,

Maintaining and troubleshooting CIS engines is not difficult to attain!!!Nor requires magic to achieve that goal. CIS relies heavily on fuel pressures and vacuum plus ignition (electrical) and compression (mechanical). The biggest problem is the lack of basic knowledge and understanding how CIS works. How do you expect your CIS to work well when certain components are bad or defective? Like in any other system, a weak link compromises the integrity and dependability for which it is designed. And I would bet that you dumped your CIS because you had problem/s with it and fed up in keeping it run flawlessly!!!! Have it ever occured to you that there was something wrong causing you all this trouble and aggravation?

All the CIS components in a 911 car from '73 to '83 could be bench tested by DIY'ers like you and me. Minimizing the quess work in CIS troubleshooting is the key like in any other investigative work to be successful. I'm no expert, but we could tell which component is good or bad in a CIS engine simply by testing the questionable part. Being able to determine which is bad or out spec is not rocket science. It only requires some basic knowledge and understanding of the subject (CIS) to know what's wrong!!!!

Tony

[James Brown]

For me, A big part is visual. We wax and clean our cars, put wide fenders on them, bigger wheels and tires. All in the name of great looks and performance. You can't get more sexy than carbs! Well maybe MFI could be MORE sexy but for the $$$$, and the reduced headaches. My CIS worked great, started all the time, hot or cold. But, approaching 40 years old, and no way to increase performance, Time to dump em in the sea. Mine is hanging from the garage wall.

[Kevin Stewart]

the 5th option do what i did put a 3.6 in, the only reason i put the 3.6 in was i was tired of the cis, Kevin

[WVU 911]

Guys, thanks for all the replies! Sorry it took me awhile to respond, I've been busy....

Tony, I did not lose the air mixture screw it was already gone when I bought the car, don't ask me how but I wasn't to happy. I didn't notice anything until I adjusted the valves and my idle starting hunting. The mixture was way out of whack.....I was able to find a screw for it after a lot of searching. I try to do as much work on the car myself as I can, I am learning as I go. I do not fully understand the CIS yet. Its a stock 82 911 SC. I do not have a fuel gauge kit, and yes I have a camera. The major problem was after I adjusted the valves, the idle was hunting and I noticed I had no mixture screw, found a screw and adjusted it so it idled good. My clutch went out beginning of last year and had a mechanic fix it. After he put it back together it was having cold start issues. I replaced the WUR, which seemed it help at the time and readjusted the mixture....this year I was having the same start up issues and got frustrated with the CIS so I brought it to a very good mechanic who is going over the whole system and making sure it is all good. I am just trying to decide, if I have anymore problems with the CIS in the future, what I want to do to it. I am leaning towards EFI. I know the CIS and motronic are very different, it's just an option my mechanic told me I could do.

There is no emissions where I live. I'm not to concerned about the cost, I want reliably, that being said I would like to also put SSIs and a 2 in 1 out M&K muffler on it.

KWC98, where did you get your EFI kit from and how easy is it to install? Besides the kit is there anything else you need?

The one problem I have with carbs is I'd have to adjust them in the winter if I want to drive my car.

Thanks again for your help guys!

Geoff

[RWebb]

OK, you want EFI then

Motec + PMO throttle bodies should knock your wallet silly

[azasadny]

Geoff,
Talk to Tab Tanner at Autobahn Garage in Findlay, OH. He took great care of me and my '74 911. He replaced my CIS with Webers back in 12/06 and I'm loving them. He can explain the options and pros/cons of each approach. In my humble opinion, there is no better Porsche guy than Tab!!

[T77911S]

the mixture screw??? i dont mean to insult you, but you are talking about the 3mm allen and not the big slotted one on the throttle body.

adjusting the valves made it run rich and it actually ran, rich at that, since it would be turned in the lean direction to remove it????

did you ever say what year it was?

[Schuey]

PMO High Performance Porsche 911 Carburetion

PMO EFI?

[DanielDudley]

Originally Posted by azasadny

I've been running Webers on my unmodified '74 with 2.7L engine since 12/06 with no problems. I drove the car 3600 miles in 6 days a few months after Tab Tanner rebuilt and installed them on my car and it's been smooth sailing ever since. Just my .02 worth...

This set up with SSIs and the MK would just make you silly happy. I remember Art going through what you are now, and then just being able whenever he wants.

You would have a very snappy car. There is no adjusting the car for winter.

I have to say that EFI is probably superior, but if you have a nice engine compartment with carbs, that is a sweet setup that everybody wants.

I have had two CIS cars, and both were stellar performers, but they had the SSIs, and then some.

What you really need is a go to guy who can take your car from A -Z. Whatever you go for, get the right guy on it. This isn't a practice session. Needless to say, you bought the car to run it. Make it run the way you want it to, and you will never regret it.