Speedfight 2 100 bogging down?

My Speedfight 2 100 has a habit of bogging down when the throttle is opened just after it has been started from cold. Usual morning routine is fire it up (starts straight away), start to open the throttle, get to say 1/4 turn, and it dies away, close the throttle and she idles happily, repeat for a minute or two, and then it finally decides that it will allow me to open her up, and she's fine from then on. Any ideas? I thought may be fuel starvation or a clogged fuel filter, but why would it clear itself after a couple of minutes? Very puzzled!