It's because you ride a YT (Yellow Turd)!
Just kidding...it's an old joke because in 97 McGrath switched to the RM250 and didn't win the championship.
For the jumps, a steady acceleration all the way up the jump and into the air is the key. Not steady throttle, but steady acceleration. If it feels too "twitchy" at high RPMs, grab one more gear but still hit the jumps with power all the way up and into the air.
Honestly, though, the jumping will come. Speed and control through the turns are much more important.
What part of SC? Where do you normally ride?