Best thing I have done in years

[75 911s]

Originally Posted by pmax

Here's a tech question ...

how do carbs handle temp, air pressure and "gravity" variations ?

You go outside and you adjust those carbs like a real man.

[930cabman]

Originally Posted by PeteKz

I'll add to dannobee's post: The book by Charles Probst, "Bosch Fuel Injection and Engine Management," contains much the same info as the Bosch manuals, and make CIS easy to understand and troubleshoot. It doesn't emphasize the problems of air leaks to which CIS is particularly sensitive, but those are problems that only become apparent after 30+ years in use, which we are well into now.

I'll agree with 930cabman that carburetors certainly give better throttle response than CIS, and I maintain that gives the impression of more power and driving fun factor. They do not produce more power measured on a dyno, other factors being equal.

Over a few years I have studied the books of Probst also "How to tune & modify Bosch Fuel Injection" by Ben Watson and "Bosch CIS" by James Weber. After checking fuel pressures and a couple cursory items there is not much available for the basic garage hack.

Also, I have years of experience with carbs

[nospiners]

Originally Posted by 75 911s

You go outside and you adjust those carbs like a real man.

Absolutly agree , practice makes perfect , more of a feel than anything .. The throaty carbyreted sound cannot be duplicated..All adjustments with cheap simple tools ..

[Louisieg55]

I think the real long term issue with CIS is that the parts will become harder to find and more expensive to replace. There are only a handful of shops or people left who still rebuild WURs and fuel distributors. Once those experts retire or stop doing the work, people like myself will eventually have to convert to carbs or fuel injection just to keep these cars on the road. Even if you have the skills and knowledge, the parts simply will not be available at an economical scale.

Tony mentioned it took him close to five attempts to get my fuel distributor dialed in correctly using different shim combinations. That tells you how precise and specialized the work is. And that level of expertise is getting rare.

Carbs are heading in the same direction. It is becoming harder to find people who know how to rebuild them well, and locating quality parts is not getting any easier either. In another five years I think modern fuel injection will end up being the most common option for people looking to upgrade or simply keep their cars running reliably.

Just my two cents based on research, talking with people, and trying to diagnose what was going on with my own car.

[Balisong]

Good post.

[930cabman]

Originally Posted by Louisieg55

I think the real long term issue with CIS is that the parts will become harder to find and more expensive to replace. There are only a handful of shops or people left who still rebuild WURs and fuel distributors. Once those experts retire or stop doing the work, people like myself will eventually have to convert to carbs or fuel injection just to keep these cars on the road. Even if you have the skills and knowledge, the parts simply will not be available at an economical scale.

Tony mentioned it took him close to five attempts to get my fuel distributor dialed in correctly using different shim combinations. That tells you how precise and specialized the work is. And that level of expertise is getting rare.

Carbs are heading in the same direction. It is becoming harder to find people who know how to rebuild them well, and locating quality parts is not getting any easier either. In another five years I think modern fuel injection will end up being the most common option for people looking to upgrade or simply keep their cars running reliably.

Just my two cents based on research, talking with people, and trying to diagnose what was going on with my own car.

How far is the cliff?

[930cabman]

Originally Posted by Balisong

Good post.

Thanks, I am lucky to have a solid unrusty example, came from the Southwest and hasn't been driven in several years due to the faulty CIS. Engine was rebuilt 6 years ago, but engine builder didn't have the tech to resolve the CIS. I am really looking forward to getting some seat time with this beauty next season.

[pmax]

Originally Posted by Louisieg55

I think the real long term issue with CIS is that the parts will become harder to find and more expensive to replace. There are only a handful of shops or people left who still rebuild WURs and fuel distributors. Once those experts retire or stop doing the work, people like myself will eventually have to convert to carbs or fuel injection just to keep these cars on the road. Even if you have the skills and knowledge, the parts simply will not be available at an economical scale.

Tony mentioned it took him close to five attempts to get my fuel distributor dialed in correctly using different shim combinations. That tells you how precise and specialized the work is. And that level of expertise is getting rare.

Not sure if you knew this, CIS is simply Porsche's name for Bosch K-Jetronic which was used in many other makes from that era.

Anyone of those "specialists" will have no trouble with CIS either.





In fact, Bosch itself offers a remanufacturing and repair service



That probably ensures these will outlast those carbs and "modern" EFI systems as well.

Originally Posted by 930cabman

I do not have a tech answer, but know all 4 of the carbureted older vehicles I own do just fine.

There can be no question to the accuracy of a modern FI system, but after testing/diagnosing CIS for several years and unable to find any local assistance, I had to throw the towel

I hear you.

I'm guessing ... and it's a pure guess ... Porsche didn't get around to a good KJetronic system until the SC era. I speculate wildly it may have something to do with the seemingly convoluted intake system unique to CIS.

Originally Posted by nospiners

Absolutly agree , practice makes perfect , more of a feel than anything .. The throaty carbyreted sound cannot be duplicated..All adjustments with cheap simple tools ..

Is that what "specialists" do ? Tune and adjust by feel ?

When the engine doesn't even fire up, how would that technique work ?

[Jonny H]

Originally Posted by HarryD

FWIW my 1973.5 CIS 911 runs great. Had it for over 20 years.

As far as I am concerned, this sums up my feelings about CIS vs Carbs.

1) The guys with working CIS systems are probably out driving their cars so they won't reply.
2) The guys that tinker with their CIS systems and have them royally screwed up will keep you running in circles with suggestions.
3) The guys that have spent a fortune on Webers will tell you they're great to justify their expenditure to themselves.

Also be aware I have two early 70’s cars with carbs. They do not approach CIS for starting and drivability.

Haha, this is funny. I'm definitely in the number 1 camp! Had my SC for 15 years now. After engine refresh, CIS parts were just checked and lightly cleaned and refitted to a new airbox ( which is now made of stiffer PA6, not ABS ). Not a single issue in 60,000 miles. No surges, no hiccups, hot or cold. Starts on the button.

Now my Alfa on the other had with it's twin Dellortos. Well, starting it is like trying to wake up a surly teenager. Once you're running it's ok - until it stalls at a junction - or idles at 2000 RPM, or spits flames in your face. It does make a great sound though!

[Showdown]

I dunno, with the ubiquity of cad, 3D printing, cost-effective rapid machining, etc… it seems like just about anything can be made for relatively cheap.

Need a specialized fitting: make 10 of them and sell the others to CIS folks here and make a small profit…

I think the real issue is being intimidated and overwhelmed….

There’s no mystery of how CIS works, plenty of books and documentation… not sure why the fear…

[Jay Laifman]

I have to put my $.02 in since you might see that I have a stupid long stream of posts on this site trying to fix my CIS. Lots of great people on this very thread helped me out. Sadly, perhaps the biggest problem was caused by my mechanic who swapped out my original fuel distributor for a late version (006) and I didn't realize it as I kept chasing down problems. Once I finally found that and got the correct one back in, it's all great again. I'm so glad I kept at it.

I've driven lots of other 911s, including carb'ed 911Ts of all engine sizes. Personally, I think my car has better power and throttle response. Carb'ed engines with their butterflies opening all at once can increase sound more quickly. I think that is what leads people to think they are getting faster throttle response.

[Funracer]

Originally Posted by Showdown

I dunno, with the ubiquity of cad, 3D printing, cost-effective rapid machining, etc… it seems like just about anything can be made for relatively cheap.

Need a specialized fitting: make 10 of them and sell the others to CIS folks here and make a small profit…

I think the real issue is being intimidated and overwhelmed….

There’s no mystery of how CIS works, plenty of books and documentation… not sure why the fear…

No fear here but CIS is so different. Been fine tuning my CIS for four years now. In spite of help from some extremely knowledgeable and generous mentors here my car runs really well, but not perfect. That cache of CIS knowledge gets smaller every year. In my six years here easy to see that. Look at posts from 10 years ago most of those posters are long gone and their experience with them.

Books and documents are great as far as they go. Going to drop my engine, again, and try and sort things out one last time. If it’s not right by next summer, my CIS will be on the Pelican Marketplace. A guy can only take so much.

[911Ren20]

going thru the same process. ITB EFI. waiting for ecu and wiring...

[930cabman]

Originally Posted by Funracer

No fear here but CIS is so different. Been fine tuning my CIS for four years now. In spite of help from some extremely knowledgeable and generous mentors here my car runs really well, but not perfect. That cache of CIS knowledge gets smaller every year. In my six years here easy to see that. Look at posts from 10 years ago most of those posters are long gone and their experience with them.

Books and documents are great as far as they go. Going to drop my engine, again, and try and sort things out one last time. If it’s not right by next summer, my CIS will be on the Pelican Marketplace. A guy can only take so much.

Exactly, not a fear but maybe a frustration. I have 3 CIS setups on the shelf and not sure if I want to offer them for sale. How much fun is a cool car if it runs like sh*^?

All that and the lack of mechanics/equipment who can diagnose this 1/2 century old stuff.

Still wished I would have done this years ago

Thanks to all posters, hit a soft spot

[montauk]

Originally Posted by Funracer

No fear here but CIS is so different. Been fine tuning my CIS for four years now. In spite of help from some extremely knowledgeable and generous mentors here my car runs really well, but not perfect. That cache of CIS knowledge gets smaller every year. In my six years here easy to see that. Look at posts from 10 years ago most of those posters are long gone and their experience with them.

Books and documents are great as far as they go. Going to drop my engine, again, and try and sort things out one last time. If it’s not right by next summer, my CIS will be on the Pelican Marketplace. A guy can only take so much.

I agree. My CIS worked well after some initial hiccups when I bought the car in 2012. While the engine was out for a new clutch, I replaced all the rubber parts and gaskets with new ones where available. I also installed new injectors, fuel lines, and other components. Once everything was back in, the car ran great—until the airbox cracked. Maybe I over-torqued something during reassembly, I’m not sure. Eventually, I threw in the towel and switched to PMO EFI/ITBs controlled by a Haltech R3. It was a lot of work but also a lot of fun. I couldn’t be happier with the results. Working in the engine compartment is quite a bit easier now too.

[Showdown]

Going from CIS to modern EFI is a no-brainer.

Going form 50+ year old tech to 50+ year old tech seems silly if reliability and ease of use are key.

If the experience of carbs is desired, then rock on with your bad self, but if eschewing the finicky qualities and NLA aspect of CIS are the goal, then the answer must be EFI.

[930cabman]

Originally Posted by Showdown

Going from CIS to modern EFI is a no-brainer.

Going form 50+ year old tech to 50+ year old tech seems silly if reliability and ease of use are key.

If the experience of carbs is desired, then rock on with your bad self, but if eschewing the finicky qualities and NLA aspect of CIS are the goal, then the answer must be EFI.

Now I am curious, how much is a budget for an EFI system these days?

[Showdown]

I posted this a while ago but froma quick search, the pricing is accurate-ish:

RHD ITBs are $2300
MS3Pro mini is $599
Wiring harness is $75
14.7 O2 controller with Bosch sensor is $135
Fuse panel is $15
Oil temp sensor is $20
TPS sensor is $50

Allow $100 for hoses, etc...
Allow $100 for wiring accessories, etc...

If you want to use Deutsch connectors, you can add $100-200 depending on what you get and how many you use...

You'll need tools but we don't count toys, er, tools as they are not project specific and will find use elsewhere.

There you go. About $3400 or so. Add MSD street fire ($175) and pertronix ($130) if you want to get rid of the CDI and points. Or if you want to delete the dizzy all together you can go wasted COP for about $200 more. (Audi 1.8 coils are about $20 each)

For under $4k you can build a very nice EFI/ITB wasted COP, sequential fuel system.

Surely you can spend $10-20k on another system and we can debate till the cows come home about the differences, but if you're not racing, the returns diminish pretty quickly.

[buster73]

Originally Posted by pmax

Here's a tech question ...

how do carbs handle temp, air pressure and "gravity" variations ?

Just took my car (3.0 with twin Webers) to the Alps up to almost 3,000 m (9,000 ft). Thanks to a dual O2 sensor setup, I was able to keep an eye on AFR-values. Idle AFR dropped from ca. 12.5 at sea level to approx. 11.5 at altitude. Unless you are doing hill climbs, you will hardly notice the difference when driving the car on mountain roads. Of course fuel economy will suffer somewhat, but you can safe fuel going downhill again .

[930cabman]

I must be really old, still like points and carbs and have a point file in every one of my vintage machines

also still on the fence with a "smartphone", why do we need this tech anyways