howdy,
The reason that your motors may not run very well when they are new or partially used is because they use dielectric(I think thats how to spell it)grease on the comm because their are no actual brushes just little copper deals you can hold the can w/ a pair of pliers and tap the armature until the endbell comes off Ive had mixed results tho cause sometimes the contact for the can breaks
but you can buy the grease at your local auto parts store (Its for lightbulbs)
Does any one know where to get the 4.2s and which one is faster?