SC distributor vacuum question

[rattlsnak]

OK, getting a 78 SC running after its been sitting for @ 8 years and have a question on the vacuum lines to the dist. The owner swears the car is original and it has one nipple on the advance unit but there are two vacuum lines dangling near it. What years had the dual advance/retard system? One of the lines has ported vacuum, (0 vacuum at idle, and goes up to @ 7-8 when throttle opened), the other line has @ 5-6 at idle and drops towards 0 when throttle opened. So it seems like the dual setup. But if i have to use one of them, I would assume to use the one that advances it when reved up.

It has some other issues as well, as in backfiring out of the exhaust under load etc, so Im going to check all the CIS system pressures tomorrow.

Its been awhile since i messed with an SC, and just cant remember!

[Bill Verburg]

The one on the back(pointing to the engine) is idle retard needs vacuum at idle

the other is vacuum advance, it wants vac. at part throttle

[vizail]

Let me see if I can help you

This is the Vacum Diagram for 1978 to 1982



This is the Vacum Diagram for 1980 to 1983 3.0L/SC



Here is a mo elavorated Diagram

[rattlsnak]

Yeah i know how they work, but didnt know which one this car originally came with, as it only has one port now. I'll just hook up the ported vacuum one and cap the other. (the timing advances when vacuum applied to it.)
Thanks..

edit...

The pictures popped up after i replied. According to them, it looks like the early SCs had one port.
Thanks!

[vizail]

By the way If you reconnest the vacum lines and properly timed at 5deg BTDC and there is a persistent fluctuation you might have a defective Ign. Dist.

Vic

[rattlsnak]

Yeah, im chasing a sporatic misfire and once i check fuel pressures tomorrow i can narrow it down some more from there.

['78 SC]

Is the air pump (emissions) still installed? One vacuum line goes to it. Sounds like you have it sorted out, but I can check the connections on my (non-Calif.) 78 if you like.

[Mysterytrain]

The 78SC distributor had one vacuum line. There should be a vacuum line on the bottom section of WUR for enrichment and another that goes to the pear shaped decel valve. All three are the small diameter hose. If its long enough to reach the distributor itmight be for the WUR.

[rattlsnak]

The other hose probably went to the air pump, as all that stuff is long gone!

['78 SC]

I traced the lines on my 78...

The distributor vacuum line (there's only one) connects on the right side of the throttle body.

There are two nipples on the left side of the throttle body, just aft of the throttle linkage. The upper one connects to the WUR (upper connection). The lower one connects to the air injection pump (now gone).

Does that match what you are seeing?

[jmohn]

Originally posted by '78 SC
I traced the lines on my 78...

The distributor vacuum line (there's only one) connects on the right side of the throttle body.

There are two nipples on the left side of the throttle body, just aft of the throttle linkage. The upper one connects to the WUR (upper connection). The lower one connects to the air injection pump (now gone).

Does that match what you are seeing?

If it's any help, my, essentially stock (air pump gone), '78 matches Steve's description.

Jerry M
'78 SC

[rattlsnak]

Yep, thats what i have, Thanks guys for looking...