'75 2.7L 911 S/C - Vacuum mystery

[Attylla]

Hello Pelicans,

When I acquired my 1975 911 with California smog emissions little that I knew how difficult it might be to restore it back to 100% OEM
911.44 in terms of 1-year only solutions must be the worst documented version of 911 ever
I am currently trying to understand how the vacuum hoses for this particular engine with Smog pump and EGR valve should be connected.

I couldn't find the vacuum layout for this particular engine anywhere not even in the WSM where 1978 onwards is covered in detail but nothing prior.



The question which bothers me is where and how is Ignition distributor retard vacuum hose connected in 1975 2.7L 911.44 S/C engine

Does it connect to the single TB port here???



Or does it connect through the T-connection to the (Blue) outside edge port at the front of the throttle body like the 1978 Vacuum layout suggests?
In this case should the port at the rear be blocked?



I've been pulling hair about this for weeks and months now.
I do hope somebody can help me out.

Kind Regards
Marcin

[Flat6pac]

The vacuum hose to the distributor connects below the butterfly because the vacuum pod on pre 78 are to retard the ignition at idle.
Bruce

[Attylla]

Hi Bruce

Both marked above are below butterfly

Regards

[fanaudical]

The distributor retard line does connect to this port:



The EGR valve connects to these two ports:



If I remember right, red goes to the bottom of the EGR actuator and the other port goes to the top.

The last small port on the bottom right connects to the vacuum actuator of the decel valve.

There are some other pics of the decel valve hose routing in this thread (as well as WUR tech references):

Sorry - Yet another CIS troubleshooting thread...

[Attylla]

Thank You fanaudical

Your thread was priceless but heartbeeaking at the same time.

Looks like all the connections are exactly as they should be.

My problem is engine bucking at exactly 1900RPM with part throttle.
Not below not above just flat spot at 1900.

The amount of ghost chasing to find an issue looks scary to be honest
Thank You
Marcin

[Walter_Middie]

https://forums.pelicanparts.com/porsche-911-technical-forum/1142452-74-us-carrera-bucking-jerking-2000-3000-rpm.html

[47silver]

On my 1975 911S, I had the same concern and I found that the the coil wire was arcing in that RPM range. I changed the coil wire but it happened again.
I have an MSD, OEM braided wires with resistors and I had a rotor that included a resistor.
i changed the coil wire twice before I changed the rotor to a non resitance type and that seemed to solve the problem at that RPM range.

[Attylla]

Originally Posted by 47silver

On my 1975 911S, I had the same concern and I found that the the coil wire was arcing in that RPM range. I changed the coil wire but it happened again.
I have an MSD, OEM braided wires with resistors and I had a rotor that included a resistor.
i changed the coil wire twice before I changed the rotor to a non resitance type and that seemed to solve the problem at that RPM range.

Interesting, i will have a look although everything including CDI, rotor, ignition wires etc is new and Porsche OEM stock
Thanks for bringing it to the table. Appreciate it

[Attylla]

Originally Posted by Walter_Middie

https://forums.pelicanparts.com/porsche-911-technical-forum/1142452-74-us-carrera-bucking-jerking-2000-3000-rpm.html

Thank You Rex
I'll add the Coil and coil wire to the checklist.