I think you got an
The Athena kit that would work looks nothing like what's on Amazon.
If that's the case, see if you can return it.
to get 40 or so, I assume you are not running the stock exhaust. If you are running the stock exhaust, maybe you're best first move after taking care of any piston/cylinder issues would be getting a performance pipe. Install that and re-jet and see if that makes you happy. Post pics of your current cylinder.
I've read a bit on the Athena kit and it seems that the general consensus is go with the DR kit as it is cheaper, performs well and doesn't require a spacer and any other fiddling that the Athena might.(edited)