L-jet ignition timing, with or without vacuum retard?, What's the REAL answer? Options

[davesprinkle]

OK, I've looked in Haynes; I've read the PP ignition timing article; I've searched this forum -- I cannot find a consensus. To set the timing on a 1.8liter L-jet car, do I remove the vacuum retard line? Or do I leave it attached? What's the REAL answer?

[Brando]

All vacuum lines to the distributor removed and plugged, 7.5º at 850±50rpms (idle).

[davesprinkle]

All vacuum lines to the distributor removed and plugged, 7.5º at 850±50rpms (idle).

Thanks for the reply, Brando. Here's my concern about this approach:

Let's say I disconnect the vacuum retard and set the timing to 7.5'BTDC. Then, when I plug the vacuum retard line back in, manifold vacuum under idle conditions will further retard the ignition. Assuming a change of 10 degrees, this would put the spark event 2.5' AFTER TDC. This doesn't seem right.

[Cap'n Krusty]

Ferpetessake! Why do you think it has a vacuum retard? It's SUPPOSED to run somewhat retarded at idle, and instantly release as the throttle plate opens.

Here's the technique, just as they taught it at the P-car school in 1973/74:

Set the dwell to 47 +/- 3 degrees, warm the engine to running temperature.
Unplug BOTH vacuum hoses and plug'em up. A couple of golf tees work fine.
Using the air bleed screw on the TB, lower the idle to 800 RPM.
Set the timing to the 7.5 degrees BTDC mark.
Reconnect both hoses and use the air bleed screw to adjust the RPM to 800-900 RPM. Once it's warmed back up and the idle has stabilized, fine tune the idle speed.

THAT'S the way it's done. If the vacuum capsule doesn't function properly, you'll need to replace it. They're NLA, but good used ones are out there.

The Cap'n

[Brando]

Dave,
Those OEM distributors on L-Jet cars have a lot of advance built into them. That's why later on they blocked off the advance line from the manifold. Listen to the Cap'n.

[davesprinkle]

Ferpetessake! Why do you think it has a vacuum retard? It's SUPPOSED to run somewhat retarded at idle, and instantly release as the throttle plate opens.

Here's the technique, just as they taught it at the P-car school in 1973/74:

Set the dwell to 47 +/- 3 degrees, warm the engine to running temperature.
Unplug BOTH vacuum hoses and plug'em up. A couple of golf tees work fine.
Using the air bleed screw on the TB, lower the idle to 800 RPM.
Set the timing to the 7.5 degrees BTDC mark.
Reconnect both hoses and use the air bleed screw to adjust the RPM to 800-900 RPM. Once it's warmed back up and the idle has stabilized, fine tune the idle speed.

THAT'S the way it's done. If the vacuum capsule doesn't function properly, you'll need to replace it. They're NLA, but good used ones are out there.

The Cap'n

10-4, Cap'n. This is just a sanity check -- I wasn't sure that Porsche would design the ignition system to fire AFTER TDC, even under idle conditions. Thanks for verifying this.