Gnarls gives me too much credit, I am studying, I'm not the professor yet though .

Last time I had this issue, as I understand it, it was a bad lead to the fuel cut solenoid on my 20r carb.  Accelerator pump could be a good place to look, I agree with that.  Float level is a good one, but I have found it's hard to screw that up.  I would also look at the basic carb settings like the idle speed and idle mixture.  Just adjust the mixture or idle speed up and see if it will run steady at too high of an RPM at least.  Then you can pull it back slowly with the ignition timing and see what happens.

I have to run thicker mixture, higher idle speed and slightly more advance to get the good  below zero cold start in the winter.  Then I re-tune in the spring time.  The point is don't be afraid to mess with these things.  The factory settings are more like guidelines than rules.

Vac leaks usually cause a high crummy idle in my experience and poor running but not no running and stalling.  I haven't seen it all though.  Vac line by the foot is pretty cheap so you might want to just replace all those 30 year old petrified vac lines with new stuff and see if it helps.

I'd replace that fuel filter and really consider the fuel pump anyway.  Maybe swap to a known good spare and see what happens.  I've had a stumbly/no idle condition from both plugged fuel filter and slightly bad fuel pump.  The fuel pump gets more action at higher RPM so it can actually get it at high RPM and not at low, oddly enough, if it's lame but not obviously broken bad.

I even had a slightly bad ignitor do this once.  I had spark, and it would run above 3,000 RPM but it would not idle or run at low RPM. 

I'm really reaching with this one...  The only other odd thing in the stock 22r stuff is the little deal that runs of vacuum that cuts the fuel a bit on decal to avoid after-fire. It's the "what is that thing" in the lower portion of your filter box that has a vac line to it. I've never had a problem with it but I guess it could cut your fuel at the wrong time if it was hooked up wrong or faulty.

Gotta just start ruling things out one at a time.