Check that all your motor wires are in good condition. Sometimes the wires can crack in the insulation or heat shrink and you won't be able to tell without tugging on them or testing with a continuity meter of some sort. If tugging on the wire, don't yank it from the bell of the motor, just give a gentle pull and feel for stretching. If using a meter of some sort, measure the three leads, two at a time looking for a high resistance. You should see something close to a short for any combination of those three leads. If the motor has multiple strands per winding, sometimes one or two of the strands breaks and you are loosing a good % of the power for that phase.
What is your motor actually doing when you pull the throttle?
Was it running fine before the problem?