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Posted by: CheeRS Apr 23 2020, 02:20 PM

Hello from paris France,
would like to learn about air lines and vaccum on my 914 2.0 GA 1974.
I do not understand why the oil vaccum breather is pluged after the buterfly with a dizzy line and the valve for deceleration additional air.
Thanks for your help
CheeRS

Posted by: Bleyseng Apr 23 2020, 02:42 PM

Look at this diagram for the hose layout


Attached image(s)

Posted by: CheeRS Apr 23 2020, 02:55 PM

About the number 9 line what is PCV ? a valve ? do not understand how this line do not make a air entry in the engine and after manifold.
What is the fonction of the line number 10 to the dizzy ?

Posted by: JamesM Apr 23 2020, 03:02 PM

Yes, on the 74 cars there is a valve on the oil tower that connects to the #9 line. If this valve goes bad or is missing you will get as described, unwanted air entry after the throttle body.

The later cars eliminated this valve in favor of a larger hose directly from the oil tower to the air cleaner.

#10 line to the distributor retards the timing under high manifold vacuum

Posted by: CheeRS Apr 23 2020, 03:08 PM

Now I understand why if I plug as it has to be this line my idle jump to 1700trs/mn
For sure, the valve is leaking.
Could I find a new one ?
alternate solution, plug this line before the buterfly, right ?

Also, why 2 differents lines to the vaccum distribution ?
One before buterfly, the second after.
the 10 to late the timing, the 11 to advance it ?
Both works in opposition ?

Posted by: jcd914 Apr 23 2020, 03:17 PM

The number 10 hose is only there to keep crap out of the vacuum canister.
The distributor only uses the vacuum retard (hose 11), so the hose 10 is attached to the vacuum canister but the other end of the hose is just tucked under the intake plenum and not connected to anything.
As the vacuum retard moves the diaphragm in the vacuum canister, air has to be able to go in and out of the advance side of the vacuum canister.

Jim

Posted by: CheeRS Apr 23 2020, 03:28 PM

Thanks, on my car, #10 is connected as the same place than #9 using a small hub

Posted by: Bleyseng Apr 23 2020, 04:50 PM

Well, that won't work as you can't have both advance and retard on the same vacuum hose. Just run the vacuum retard hose as per the diagram as the distributor is a mechanical advance unit (the weights are inside) and you would need a port on the throttle body to plug in the advance hose thats above the throttle plate.
The PCV is positive crankcase ventilation valve to suck the pressure out of the crankcase. If this isn't connected then the crankcase pressure has nowhere to go and gaskets and seals can leak, mostly the valve cover gaskkets.