you MAY be missing a circlip from hopper number 2... a simple test, is to switch both hoppers on, and turn them upside down, if hopper number 2 spins faster when inverted, then a circlip is missing from under the cone. give it a try.
if its STILL slow, then its most likely the motor. but to figure out exactly where the problem is, strip BOTH hoppers down, and keep switching parts between the two, to locate the problem.