Enlightend beings don't make more good or neutral karma? Does a Buddha or Arahant not make good or neutral karma? If somehow an enlightened one does make karma does it immediately come to a result? Are all the actions enlightened beings  do the result(vipaka) of previous good karma while on on the path to Nirvana? Is all the enlightened karma neutral?
In its essence, "kamma" means "action" with attachment. 

While the suttas do refer to "kamma without attachment" namely, "neither-dark-nor-bright kamma" (AN 4.237), this type of kamma is also called the "kamma that ends kamma" (AN 6.63). Therefore, it is not really "kamma". 

the essential meaning of "kamma" is "action with attachment", as follows:


  And what is the right view with effluents, siding with merit,
  resulting in acquisitions (attachment)? 'There is what is given,
  what is offered, what is sacrificed. There are fruits &amp; results of
  good &amp; bad actions.... 
  
  MN 117


Refer to Bhikkhu Buddhadasa PDF booklet: Kamma in Buddhism