C. I. S

[dipso]

Quick question hopefully.
I have a 75, 2.7 . I have been reading a lot about the mixture screw near the fuel distributor and was wondering if it would hurt any to fine tune it.
The car runs fine, no problems on start up, idle or anywhere.
Just looking for a little more performance-horsepower.
I am sure the mixture has not been set in at least 130,000 miles or 14 years.
I should not do this without the proper equipment, if it is already running fine, correct? I see there are gauges for this operation, as well as the turn until it stalls and reverse method.

I would like to do this myself, I enjoy learning and working with this car.
Could I screw things up or is it as simple as putting the screw back where it was if I don't like it.

[Paulporsche]

I guess it depends on what Dirty Harry asked that guy, "Do you feel lucky, punk?". It looks like you've been searching so you know the adjustment procedure. It's just that you have never done it.

You'll need a 3mm Allen wrench about 4 3/4" long. Usually if you go slightly richer, you can pick up a slight increase in hp, but that might only be noticeable @ higher revs. Of course you can always put the screw back where it was if you don't like the new setting. You just have to pay attention and be mindful of where it was. Some screws are indexed by means of clicks you can feel while turning. but I'm not sure if the 75s have that. Whatever you do, always make your final adjustment going from lean to rich.

You can always have a shop w/ a gas analyzer check it , let you know where it was, and then set it anew. JW recommends about 3.5%. Most shops charge very little for this.

You should also make sure all your ignition components are up to scratch. And be sure your airbox has a popoff valve. Make sure your injectors have a good spray pattern and your fuel and control pressures are correct. Finally, be sure you have no vacuum leaks.

In your case, if your 2.7 hasn't been touched in 130000 mi, I would think that the overall condition of the engine would be more of a factor than the CO setting in determining hp and performance.
.

[Johnb911]

I would check out all the other things as Paul Porsche recoomends.
Find the leaks, clean and replace innition components.

Don't mess with the CIS inless it's the final link in the chain and something is still wrong.


Just My Two cents. (CDN) EH!

[Jay Laifman]

Don't touch it. If everything is good, then everything is good. You're not going to find 10 missing hp. I've been forced by necessity to have to adjust it. Let me tell you, it's a huge pain, and can be a real nightmare when you aren't exactly sure where it was before when it was good. In fact, I've had it where it wouldn't even start and you're just swimming blind as to which way to turn it to get it to start! That's no fun!

Maybe if you are really curious, take the car to a local smog shop and have them pull a reading of your CO% at idle and at 2,500 rpm. If it's way out of wack, then think about it (but as mentioned, after you know everything else is set right). My local smog shop lets me do it for $10, or free sometimes, and they let me tweek it right there while it's on the sniffer.

But, again, if it's all good, don't assume you can make it better by going in any direction.

Nightmare, nightmare, nightmare.

Are you off this idea yet? Or do I have to scare you some more?

[Walter_Middie]

I agree not to adjust the CIS if you don't have to.

If you want to find hidden HP, your best bets are to check that full throttle pedal opens the engine throttle all the way. The other most often overlooked item is the distributor advance. Make sure you are getting the mechanical advance you are supposed to.

[ossiblue]

I agree with all who are trying to discourage you--if it runs fine, leave it alone. If you want to "fine tune" it, you will need the necessary diagnostic equipment. Since your car hasn't been touched in 130K, I'd suggest you find a good, friendly Porsche expert to fine tune all components, and who will let you watch the process. Once your car has been dialed in by an expert, you will have a base line on the performance of your car, as well as an evaluation as to what it may need. Messing with the CIS is something I think you'll want to think twice about.

[dipso]

Sounds good," If it's not broke don't fix it" right.
I have brand new injectors, they made a big difference.
What ignition components do you suggest I replace or inspect. Same story on the mileage and age on those parts too. Could be even older.

I am the second owner of this car and the previous owner had the engine rebuilt at 130,000. The car now has 250,000.
I bought the car 14 years ago at 175,000.