Cogging happens for a few reasons. Low end batteries are common cause of cogging. 2ndly is poor battery connectors is another reason. If the battery is not charged up to full power can cause cogging as well as the receiver not getting enough power when you first his the throttle will casue the car to stutter.
In this case I would bet if you use a better battery it will stop doing that.
With all the new brushless systems coming out and the price of cheap Nicads or Nimh packs coming way down because of lipo packs this is becoming more of a commen problem.
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