81 SC Ingnition Timing
 

I have a question about the ignition timing on an 81 SC. The distributor has two vacuum lines for advance and retard I am guessing. The one closest to the distributor shaft is routed through a switch and then to the intake. The one on the front is routed directly to a port on the back of the intake. If I remove or squeeze the one routed to the electrical switch, the car idles faster. If I remove or squeeze the other one nothing happens. Is this normal operation at normal operating temperatures? I want to amke sure the advance unit is working correctly first.

I reset the timing when I installed an MSD but did not follow protocol and disconnect the vacuum hoses first. So, I figured I woudl go back and re-set it again correctly assumign it was now off by some margin. Do I remove both vacuum line leave the idle as is (it's ~950 before removing hoses) adjust the timing to 5 deg BTDC and then reconnect the hoses or do I re-set the idel to ~950 with the hoses diconnected?

Thanks in advance for the advice. I searched everywhere and Bentley's only tells you what RPM, to remove the hoses, and timing setting. Ther eis not much out there about correct procedure and the correct routing of the vacuum lines.

Removing one will do nothing, so you can remove it....or not....doesn't matter. I thought the other one would decrease idle when disconnected. At least, that's the way it works on my '83.

but the real way to time a 911 is at full advance. with all vacuum lines still plugged in, you open the throttle until ignition timing stops advancing. that will be some where around 4000-5000 rpm. At that point, timing should be about 35 degrees BTDC. You need a timing light with the advance feature to do this. Then drive it. If it has a detonation problem, then back it off until the detonation just goes away, and then maybe another degree or two. Often, they will not detonate at 35 degrees BTDC. Mine does not. This winds up being about 5-7 degrees more advanced than stock spec. Makes more power.

As SuperJim has said, and this with fresh gas of the proper octane.

John

Thanks for the reply and suggestions.

Are each of the vacuum lines going to the correct side of the advance unit? (i.e. the one going to the electric switch goes to the back end of the advance unit). I am now curious since pinching or removing the one hose speeds up the idle instead of slowing it down.

OK, scratch the last question. I reversed the hoses and the throttle was anything but responsive. It ran but did not accelerate well. I am guessing they are hoode up right and not reversed. So, per your suggested method, I am going to see if I can find a buddy with an advanced timing light to do this with. If not, I'll mark off 35 degrees on the pulley using a wax pencil (7X the distance of the 5 degree mark) and do it that way using my standard timing light. Thanks again!