Hi Rob,
Do you mean when up in the air or on ground? I have a Ros 125..........starting from cold, prime only a couple of times and then start with throtte WIDE open, as soon as it kicks in ease off the throtte. When hot start (actually you probably do mean when-in air) then kick start with styrrup but make sure you dont depress the throttle ie leave it open......when it catches blip it and you are away.
Works everytime with me.
hope this is of help?
Mike