Lrp sphere juddering

[Rcnoob]

Hi guys, i'm having a problem with my lrp sphere, its hooked up to an lrp x11 7.5t motor and i dont know why, but it keeps juddering at lower speeds and when i apply full throttle out of a turn, a very helpful man, going by the name of Tony mulligan, who sorted me out with a new capacitor, however that only had short term effects, so i was just wondering whether anybody had an idea as to whats going wrong, thanks ( running 27mhz btw )