82SC Ignition Timing with and without Vacuum - Why so different?
 

I just got done checking the idle timing and It makes me wonder what is going on with the vacuum lines?

Per the manual for the 82SC, 5deg BTDC at 950 rpm, with the (2) vacuum lines disconnected.

After I reconnected the (2) vacuum lines, and just for curiosity I check the idle timing. The timing jumped to ~5-10 deg ATDC! About 15 degrees additional retardation.

The 78-79 SC says 5 deg BTDC with the single vacuum line connected.

Since I only had to tweak the distributor ~2 degrees to get it in spec. I know I did not fundamentally change the timing. So this is how the car runs.

But why did the (2) vacuum lines cause the idle timing to jump so much? Can anyone explain what is going on in the 80-83SC distributor and why?

At idle the advance line won't matter. When you reconnect retard it should change timing by 5 degrees.

Actually found the Bentley Manual is in error. 78-79 SC should be checked with it's single vacuum line removed. Bad error...

So the retard circuit is retarding timing when the throttle is closed (high vacuum)