Causes for lowered gas preformance?

[neptunonc at yahoo.com (Neptuno)]

Like the tittle mentions:
   
  Quick people what are the main causes for lower gas performance?
  The car is running smooth. There is a leak at the muffler, but does that matter?
  It was timed last this past summer at Dan Bubbs or was it last year?
   
  Thanks,
  EL Tony

 __________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 
http://mail.yahoo.com