Eroisin

Can someone explain how the timing advance works on a 78 SC. I cannot see any tubes or hoses from the distributor. There is a green wire connecting to a what appears to be a pickup for the ignition unit. My user manual mentions a vacuum arrangement taht should be disconnected when setting the timing but, I cannot see anything.

Tks in advance

Locky

Steve Weiner-Rennsport Systems

Locky:

You should have a vacuum cannister on the side of your distributor with a small hose that connects to the throttle body.

Send me a picture if possible.

theiceman

I had this picture in my files ... not great but may help.
I have an arrow to the vacuum tube and the vacuum canister.

Greg D.

Here is a better picture, assuming my distributor (83) is the same as your 79



If you do not have this apparatus, it was either taken off and replaced with a non-vacuumed operated distributor, or it was not the same in 79 as it was in 83 - I have no idea... But there you go !

On my car, you disconnect both those hoses and check them for vacuum on a wet finger - or your tongue if you are adventurous and like the taste of old rubber or placing your head near a moving fan - your call, I prefer the finger !

Unplugging them lowers the idle, so you raise it a bit with the idle screw, then shoot a timing gun at the car. I recall 5 degrees BTDC or something +/- 2 at idle and a very low number at higher RPM (something like 25, unlike most older 911s which had much more advance). Check the specs on this site or in a book. If you need to adjust, you loosen the distributor locking bolt (seen here under hose A, can you see? ;-) and pivot the distributor body, and reshoot. Once done you reconnect and retighten it all and re-lower your idle to the correct settings... At least that's on my 83 !

I'd check your distro # against the PET to see if the part is the right one !

theiceman

the 78 and 79 do not have the second vacuum hose. If I remember correctly it had something to do with helping change the timing for emision controls or something but not positive.

Peter Zimmermann

'78/79 SCs have a single vacuum line for vacuum advance. The line remains in place when timing is set at idle (5 degrees BTDC @ 950 +/- 50 rpm), but should be removed to check timing advance (26 degrees +/- 2 degrees BTDC @ 6,000 rpm). '80-83 cars have two vacuum lines, a retard line (nearest the fan housing), and an advance line. To check/set timing on these models you must disconnect both lines, then, by using the throttle body idle speed screw, slow the engine to 950 +/- 50 rpm, and then set the timing (5 degrees BTDC). Oil temp should be at approx 176 degrees F on the early cars, and 194 degrees F on '80-83 models.
Pete

Eroisin

Aparently some SC's were shipped without the vacuum apparatus - mine included.

Pete - you may remember posting help with advice on re-installing the distributor back at xmas time. I got it running fine - except the idle is a bit high. Tks

Tks to everyone.

Locky

theiceman

so how does the timing get advanced ... centrifugal weights ?

Eroisin

apparently - yes. I have not taken the distributor out (again) to confirm as it is running well