Wonder what it was mounted on, Carrier, scale,  free flight?

   That is t6he beginnings of a Bill Johnson modified throttle set up. To be complete, there would be a bell crank on the back of the engine that would push the slide open at high throttle and close it at low throttle. There was also a fuel metering device incorporated into it to cut back fuel at low throttle because the engine would be on crank case pressure. Properly set up and adjusted it worked quite well until good carburetors came along.If you never met Bill Johnson, he was quite the character. he was from the St. Louis, MO area, and Ii got to know him later in life as he used to come in to the hobby shop I worked part time at all the time. I found out later that as a kid, he lived an easy walk from my house and I never knew it! He also had an ingenious  retract system that worked off of centrifugal force and it was detailed in Aeromodeller magazine, I believe. Any carrier veteran from back in the 60's, 70's and 80's will know Bill Johnson.
  Type at you later,
  Dan McEntee

Thanks for the replies, that is so cool, we really are a resourceful bunch aren't we.