Deceleration valve?
 

I'm trying to identify a valve that controls the manifold vacuum in a '79 SC. The deceleration valve is supposed to slow down the vacuum enough to keep the idle from dropping (from a high RPM) below a point where it stalls. Is this the valve?

Sorry, the image didn't work the first time. I'll try again:

That's it! I always assumed it was there to keep the engine speed from dropping too fast when one lifts the throttle and dumping a bunch of unburned gasoline into the exhaust. I think it's main purpose is emissions control. Jim

Exactly, Jim!
It's another annoying little part, that is easily disabled by removing and pluging the vacuum hose that connects to it.

Thanks guys!

I can see the adjustment on top of the valve. But, how do you determine the correct setting?

Do a search; I seem to recall John Walker explaining the adjustment sometime in the past. Jim