Arturus;
Damping Oil squirting from the vent simply means there's a bit too much...eliminate by holding a rag over the hole, and with Air Cleaners removed, manually lifting the Dashpots to their maximum height once or twice...all extra oil with shoot into the rag...done...reinstall AFs.
CS; I don't feel as strongly about not using ATF...because our practical viscosity tests long ago showed it was quite close to 20W, and as it is used with wet clutches of the automatic gearbox, we know it has very good temperature operating range, so that's what we have used (with good result) ever since. ...and I can't really agree about SUs "wearing"...the Damper Valve(2) is 1. ... always submerged in Damping oil(1), and therefore 2. ...makes NO contact with ID of tube..., and 3. ...a film of Damping oil also serves to separate OD from ID of Dometube (at (3))...so there is no contact there...and where there is no contact, there can be no wear...thanks to the brilliant design...it's true!
(...unless things were completely dry...and that doesn't happen with even the most neglectful owner, because even when completely neglected, there will always remain a small amount of oil in the bottom of tube, but IF it were to get completely dry, then Dashpots would soon thereafter freeze in place, and engine would not run, or run so badly, even the most neglecting owner would soon realize something was very wrong...and hopefully check it out!) It does emphasize the point that Damping oil is important!
See also:
http://www.sw-em.com/su_carbs.htm#Da...20of%20Dashpot
I Love SUs!