1978 Charcoal Canister w/o VCV or VSV

[Grayscale]

Is there a Vacuum Switching Valve on the driver's fender? My intuition is that you will have a barb on the intake that serves as a controlled source of vacuum for emptying the fumes from the tank, it also is likely a flame-arrestor in the event of an intake backfire. Right now, it looks like that spot has a tube is going to the PCV valve on the other side of the engine.

@Engineer8000 Thanks for the diagram. Notice the lack of an EGR tube on the carb, no fuel return line, and the lack of a Throttle Positioner diaphragm. From that, it is safe to say that there is only one barb on the valve cover side of the carburetor, hence a non-USA carb, so there will only be one-ish BVSV, and its source of vacuum is the brass barb at the base of the carburetor (about 3mm - outter diameter). Which barb on the Vacuum Control Valve goes to the Vacuum Switching Valve (the big one)? If he doesn't have a Vacuum Switching Valve I think that might be where the simpler 'purge valve' that @zerotreedelta mentioned comes in.

 

[zerotreedelta]

The photo with a bit of the "why" labeled".

As far as the vacuum-signal source, it'll be similar to the one that feeds the dizzy advance...you could even tee that line if your carb only has a single "signal" port. Newer purge valves also seem to skip running that vent line to the air cleaner...I suppose Uncle Toyota was a bit more cautious about harsher environments.

 

[tmckeon]

Looks like I have no other option than to install a tee on the PCV line so I can access strong vacuum to hook the VCV to. Tee-ing into the PCV line has been mentioned in this thread as a possible option and I’ve read a few accounts of others doing this.
Does this sound like a safe option?

 

[Grayscale]

You have options: a pipe plug on the front top side of the intake manifold, also, the rubber plug under the carb in post 17, labeled, "from VCV?".
Someone probably has the proper used barb with the tee for the hose. I bought my rig with most emissions installed, and there was a special tee where you could blow air thru it, but a flashlight, or pin, didn't go thru it - I'm thinking about the possibility of intake backfire.