Hey Mike you and I have the exact same setup.
Tecno estoril
75cc polini
19mm phbg
mallossi round airfilter
This is what I can tell you:
I had the same thing happening I would hit 45 and it would do this weird fluttery jerk shit I had no idea what it was, So I carefully went from a 99 all the way down sequentially to a 84 jet, in the top end I was cherry, but my mid range was shit and I seized my kit :( so sad, so next I put it all back together and raised the needle 1 slot, now it sits at one up from the bottom, the mid range still fells a bit lean, but the kit is fucked anyway so I am experimenting like a fuckass to get this to work, I am going to up the needle one more to give it a little more juice and see how she rolls, This set up is a bitch to tune for whatever reason, lets figure this shit out!