85 XJ700-X Looking for some extra pony....

I pick up this bike late this summer and have logged over a thousand miles on her. So far so good. Took her to 130 mph a few times without much effort. I have only added a K&N filter. I'm not lookint to do something too drastic. Just wonder if I can do something simple and cost around 400-600$ to gain some decent hp. I currently get around 90 to 100 miles to reserve and would like to keep it this way if possible but wouldn't mind loosing a few miles/gal. Give me some idea on what I could do in my off season to get her scootin better next season... Bike is 15xxx miles and no known issues. Thanks.

 

I like the 4 to 1 exhaust system on this bike....

http://maxim-x.com/pix-raywoods.html