I read somewhere that the F7 emulsion tubes would help with the momentary stumble. I believe that it was to help with the stumble between the primary and the secondary opening, not from starting from idle, but I could be wrong. I think I read that here on the FAQ, but a quick search didn't pull up the thread. My carb had F66 tubes in it, but I replaced them with F50s and followed the prescription. HTH.