MFI adjustment

[gdriver56]

Hi everybody,
this is my first e-mail as I have registered this morning !
I have just bought a Carrera 2.7 european specs, with the MFI. One problem I have noticed is a "hole" at 2.800-3.000 RPM and I assume the reason is not electrical as the car has new points/spark plugs/leads etc.
I believe it should be the fuel adjustment and I plan to set it right with the help of my mechanic.
I cheched on mr. Wayne's book 101 projects... and it says that the adjustment of the fuel delivery screw shouldn't be done with the engine running.
Does anybody have a clue on why the adjustment has to be performed with the engine switched off ?
Any other suggestion to eliminate the hole in the carburation ??

Thank a lot in advance

[Jim Richards]

Because the tool you use while standing at the aft end of the engine is passed through the fan (between the blades), then it pokes out a hole on the engine shroud and finally engages the adjustment point on the MFI injection pump. As you can imagine, going between the fan blades while the engine is running might be problematic.

I have just bought a Carrera 2.7 european specs, with the MFI.

Man, do I envy you.

By the way, what type of muffler is on your car? The reason I ask is that it's been mentioned many times before on 911 Technical Forum that MFI cars using aftermarket mufflers exhibit a flat spot at similar RPMs. You may not want to cover up this issue (if applicable) by richening the MFI.

[gdriver56]

Thank you Jim,
how stupid of me!
I once had a 2.4S and I thought I had enough of old, rough, mechanical stuff..... wrong!

Francesco

[Rot 911]

Here is everything you will ever need to know about your MFI: http://www.pelicanparts.com/techarticles/911_MFI/TipMFI.htm

[gdriver56]

Kurt,

great hint !

thanks a lot !

[Baurice]

Hi there!

Like yourself, I have a "rest of world" spec 1974 carrera 2.7 i.e. a '73 RS car drivetrain in a '74 body.

When I got the car it was way out of tune and I have had to spend quite a bit of time (and money!) on it!

Points to note for my experiences
1. As I understand it all these cars have a "hole" at just under 3000rpm. It is a characteristic of the MFI unit. As the local OPC master mechanic pointed out, the 3D cam on the MFI unit is race derived, comproming their road smoothness. Sure enough below 28000 and over 3000 rpm my car is very smooth but there a slight hesitation between these. It is just the way they are!
2. Before u start on tuning of MFI please please take the time to do the "10 demandents" (see Lee Rice's article and OPC tech articles). There is absolutely no point in tuning the MFI until these are all as perfect as a 29 year old setup can be. I thought that these "demandments" were all OK on my car and was about to send the MFI unit on my car off to the UK for a service (a major expense from NZ). I checked these very, very carefully and sure enough the car smoothed out markedly and the MFI unit itself needed no tuning
3. Enjoy the car - the ROW/European car is very underrated, being tainted by the US spec'ed cars reputation for overheating. It is nice to be able to experience what is essentially a 73 RS for a fraction of the price!

[derek murray]

Download the document "check, measure, adjust" from the link below in my signature area... its a nice clean, high resolution copy - 2.5MB

Good luck.

[gdriver56]

Originally posted by Baurice
Hi there!

Like yourself, I have a "rest of world" spec 1974 carrera 2.7 i.e. a '73 RS car drivetrain in a '74 body.

When I got the car it was way out of tune and I have had to spend quite a bit of time (and money!) on it!

Points to note for my experiences
1. As I understand it all these cars have a "hole" at just under 3000rpm. It is a characteristic of the MFI unit. As the local OPC master mechanic pointed out, the 3D cam on the MFI unit is race derived, comproming their road smoothness. Sure enough below 28000 and over 3000 rpm my car is very smooth but there a slight hesitation between these. It is just the way they are!
2. Before u start on tuning of MFI please please take the time to do the "10 demandents" (see Lee Rice's article and OPC tech articles). There is absolutely no point in tuning the MFI until these are all as perfect as a 29 year old setup can be. I thought that these "demandments" were all OK on my car and was about to send the MFI unit on my car off to the UK for a service (a major expense from NZ). I checked these very, very carefully and sure enough the car smoothed out markedly and the MFI unit itself needed no tuning
3. Enjoy the car - the ROW/European car is very underrated, being tainted by the US spec'ed cars reputation for overheating. It is nice to be able to experience what is essentially a 73 RS for a fraction of the price!

Dear Baurice,
sorry for the delay in replying but I was away from civilization the last two weeks !
Indeed I this you are right because I once had a 2.4S and the same problem was there at around 3.000 RPM in spite of a full MFI pump rebuild at BOSH in Germany!
I have checked some of the demandements but I still have others to measure/fix.
Hopefully at the end it will be fine.
I believe these cars have already started to climb given their mechanic and the total number built of about 2.000.
In France and Germany the asking price is already in the range of 25/30.000 Euros!! Crazy isn'it ??

Thank you and best regards

Francesco

[Baurice]

Hi Francesco,

Good luck with your car!

There were only 1038 produced in 1974 and 538 in 1975 so it is actually as rare as a 73RS!

I think that the price will continue to go up for the Porsche aficionados. It just makes my smile wider then I drive mine!

Andrew

[Matt Smith]

Hi Andrew. I like those ROW 2.7's too..

Are you in Akl? That flat spot can be removed with a bit of twiddling.

[Baurice]

Hi Matt
Sorry for the dalet but just got back from hols.

No am in CHCH. Do you know of any good twiddlers dowm here?

Andrew

[Baurice]

Correction:
Sorry for the delay.....etc

[jluetjen]

1. As I understand it all these cars have a "hole" at just under 3000rpm. It is a characteristic of the MFI unit. As the local OPC master mechanic pointed out, the 3D cam on the MFI unit is race derived, comproming their road smoothness. Sure enough below 28000 and over 3000 rpm my car is very smooth but there a slight hesitation between these. It is just the way they are!

Forgive me for being blunt but --- No, that's not true.

I've got the stock MFI in my '69E and the car pulls cleanly from below 2000 RPM right through 7000 RPM with kick when the engine comes on cam at 4000 RPM. A properly tuned MFI will run better then anything but a modern mapped system. Porsche and Bosch developed different 3-D cams for different applications. Your car has no more of a race designed cam then mine does. The MFI's 3D cams do seem to be related to the engine's cams, so ideally you'll want to use an E 3D cam with an engine using E cams, and so on. I've also heard of a number of people making do successfully with an E 3D cam and S engine cams, or a T 3D cam and E engine cams.

The most common reason that I've heard for a flat spot at that rev range in an MFI'd engine is the use of an aftermarket sport muffler or exhaust. Making this change affects the engine's air flow and as a result the MFI (which is a mapped system) will go lean at certain rev ranges. I don't see that you've mentioned the exhaust system that you have.

Alternatively, have you confirmed that the pump is the correct model for your car?

I'd also check the ignition timing across the rev range and make sure that the distributor is moving the spark timing as it is supposed to.

[gdriver56]

John,
thank you for your contribution, I am still working on other things, as I finally decided to restore the whole car. Certainly it seems logical that things should work properly once all settings are the correct ones.

Take care

Francesco

[70SWT]

Not trying to hijack the thread, but I do have an MFI question.

As I feebly crawl forward in accumulating 911 knowledge, I have found that a 2.7L engine I bought, out of a 75 911S, has the 1972 911T MFI system installed. Supposedly, this engine pulled quite strongly when installed. Waiting to clean it up and install to see on that...

My question is, is the 72 T MFI system suitable for the 2.7L? I read in the Pelican MFI section that an original problem with the 72T's MFI was that it was too rich for the displacement. I wonder if it would therefore be better suited for the bigger engine? Anybody running this combo?

Hopefully this won't get lost at the end of the thread - may have to relist...

TIA Al