Uhmmm...I think he said he's got a 1980 CB750SS. That would be the CV carbs. And I think the spring he's referring to is on the inside of the vacuum diaphragm (under the cylindrical cover on the carb top). Should be an easy find if you go to
http://www.bikebandit.com, put in your year/type/model of motorcycle, then go to Carb or Fuel System. They should also stock the spring for you.
Examine your diaphragm carefully, as a little nick or hole or tear will cause problems. Be prepared to pay a little if they need replacement. It may be cheaper to find a carb back on EBay or your local MC junkyard, but caveat emptor is the catch phrase here.
Luke M
Used to have a 1979 CB750L, sold it as a parts bike, now riding a slightly modified 1984 VT700C. Network/Field Engineer. Central OH, USA, Earth, Sol System, Milky Way Galaxy, Universe.