im buying a 2003-2005 yamaha yzf-r6 and i dont know if there is a difference and i dont want to sound stupid but is there a difference between yzfr6 and just a r6

As long as it is just the YZFR6 and not the YZFR6S it's the same bike everyone commonly calls the R6. YZFR6 is just the full official model designation/name.

try and get hold of a fuel injection model