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JFairman JFairman is offline
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Join Date: Jul 2006
Location: S. Florida
Posts: 7,289
"This does not really make sense as they both are essentially going to the same place so retarding and advancing at the same time when the switch is open...I think...???"

It does make sense because the top port is just above the throttle butterfly at idle. That one is the vacuum advance port and being above the butterfly at idle it doesn't see any vacuum so there is no vacuum advance then.

The bottom port is below the butterfly at idle so it sees full manifold vacuum at idle and that one is the vacuum retard port on your '86.
Configured like that the motor gets vacuum retard at idle and gradually looses it as the butterfly opens. It always sees some vacuum from the venturi effect of the throttle body until boost comes on, then it sees boost air pressure.

As you accelerate and the butterfly opens the top port becomes exposed to intake manifold and venturi effect vacuum and that makes the timing advance as long as the red vac advance hose is connected to the outer vacuum port on the distributor. That line is origonally red fabric covered and it goes through a mechanical thermo valve on your catalyst equipped 1986 car before it goes to the outer vacuum advance port on the distributor.

The purpose of that thermal valve under the airflow meter housing is to block vacuum advance until the motor warms up, and blocking vacuum advance retards timing and that raises exhaust temperature so the catalytic converter heats up faster and the car passes USA emissions allowing the 930 to be sold in the USA again in 1986.
That thermo valve lowers engine performance making the car more sluggish getting away from a stop because it removes vacuum advance until the motor is hot and if you don't have a catalytic converter then bypass it because it has no purpose then and should definately be bypassed.
You still have mechanical centrifical advance in the bottom of the distributor so there is always a little advance going on as rpms raise to around 3500 but it's not much.

The 12 volt vacuum solenoid in the second picture you mentioned goes in the blue vacuum retard line and it is there to block vacuum retard from going to the distributors inner retard pot for the fist minute or 2 after a cold start so the timing advances a little at idle to help raise the idle speed about 300 rpms.
When that valve opens and vacuum retard comes back, you'll notice the engine abruptly drop about 300 rpms. The auxilliary air valve that bypasses air around the throttle body when the motor is cold also raises the idle for a minute or 2 after a cold start.

Don't knock the hose/cotter pin removal tool till you try it...

It is made for water cooled engines that have not had a radiator hose removed from a cast aluminum fitting in years and the corrosion in the aluminum under the hose has stuck it on so you can't just pull or twist it off.
You push the rounded off pointed end in between the hose and corroded fitting and work it around the circumfrence to seperate it from the fitting.

It also helps to install stiff rubber hoses in tight areas like that CIS intake elbow hose if the blow off manifold is bolted in place.

It also prys out cotter pins easier than anything else and if you are mechaically inclined you will discover many other uses for it.
Old 09-20-2010, 07:33 PM
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