Hey Rajin_Cajun,
have you sorted out this issue as yet??
I 've got a SNR...which i believe is based on the HPI MT...i had a similar problem...what I did was center the Throttle trim on the transmitter first the then put on the servo horn then before connectin the throttle linkage to the carb I adjusted the throttle arm(on the carb) so the ball is positioned in line with the linkage. ( if this causes the opening to be bigger than 1mm what i did at this point was to loosen the screw on the side of the throttle barrel and reposition the arm so that when at idle(neutral) there is a 1mm opening. remember to tighten the screw properly.once you done this connect the throttle and brake linkage and use the throttle trim on the transmitter to fine tune..lemme know if this helps out