On Thu, 5 Oct 1995, David Schwarze wrote:

> Alistair Bell writes:
> > 
> > Isn't there a vacuum line(s) running from the distributer up to a small box 
> > attached to the top of the engine compartment? I can't remember which way 
> > it alters the timing, but it gets an electrical signal from the tranny 
> > that opens/closes a valve controlling the aforementioned vacuum line(s).
> > 
> > David Schwarze help me out here ;)
> 
> Uhhh... I don't no nothing bout no steeeenking vacuum line! :)  Not on a
> 73, anyway.  I'd say that the van isn't running right.  I'd check the
> compression first, and then check to see if the emissions were in line.
> 

OK David, you're right, "don't look for zebras when a horse is to blame", 
but there IS a vacuum line.

Page 65 "Engine and Clutch" (Bentley Official Service Manual, 
stationwagon/bus 1968-1976)

"Checking Vacuum Advance Cutoff"

"Except for 1974 models with manual transmissions, all dual-carburetor 
engines are equipped with an automatic vacuum advance cutoff. the cutoff 
valve is electrically operated by a switch on the transmission and a 
temperature switch. The system is shown schematically in Fig. 19-5.

(Schematic...showing a vacuum line coming from the right hand side of the 
vacuum advance housing on the distributor, to the two-way cutoff valve. A 
vacuum line also goes from the cut0ff valve to the carb (left hand one). 
Power from "15" (from coil), runs to the cutoff valve, exits and goes to 
a temp sensor and a switch on the trans)

Except in 4th gear, the vacuum advance is cut off whenever the air 
temperature is above 12C (54F). This means that the vacuum advance is 
only effective in 4th gear and in all other gears at temperatures below 
12C(54F).

To check cutoff:

1. Following instrument manufacturer's instructions, install a tachometer 
and a stroboscopic timing light.
2. Run engine at 200rpm and direct the flashes of the timing light on the 
mark on the crankshaft pulley.
3. Have someone depress the clutch pedal and engage 4th gear - keeping 
the clutch pedal depressed so that the vehicle does not move. At the 
moment when 4th gear is engaged,the timing mark should move about 30mm (1 
3/16 in.) to the left. If not, there is trouble in the vacuum advance 
cutoff system.

Alistair