hey im actually havin the exact same problem, i to have a brushless upgrade, this morning when it spooled up it was fine, but completly out of alignment, so i adjusted the servo's got it all fixed up and now when i throttle up/or down, just like the idle speed i'd guess you call it, before its goin fast enogh to take flight, it vibrattes like crazy and jupms everywhere.. its just a specific throttle range. one i give it a little more throttle it it levels out and is fine.. i've flown every size of heli and never had this happen before, nothing is off balance so i dont know why i would do that..im also having problems with my tail, no matter how much trim i give it it the stock tail motor cant keep up with the brushless motor, and it just spin's in circles.. i'm thinking about uprading that though