Image: 1938 or 1939 scooter from http://salsburyscooterscrapbooks.com/Models40thru60/
“While Foster [Salsbury] had a marketing hit on his hands with the 1937 Aero, Foster and his team kept innovating new approaches to make the scooters easier and better to ride. Foster’s biggest innovations hit in 1938 and 1939. He and his team innovated the starting clutch, which made it easier to start the scooter and keep the engine running even when the scooter came to a stop. So you didn’t have to restart the scooter at every stop sign and red light. He and his team also innovated the variable speed or automatic transmission, which was an incredible breakthrough – something that Vespas would not have until decades later. With the variable drive transmission, the rider doesn’t need to shift gears using a hand-lever clutch and a twist grip. The variable drive transmission made riding a scooter MUCH safer and easier.”
Excerpt from Salsbury Scooter Scrapbooks image link above. There is a tremendous amount about the Salsbury scooters at that link. Later, there was a new owner and a factory in Pomona, CA.