You epoxied the exhaust valves open? And you want more mid-range power? I don't have exhaust valves, but I thought that the point of the exhaust valve was to give you a good mid-range and then a kick at the top. Wouldn't removing the epoxy and keeping the exhaust valve clean and operational give you the mid-range that you're looking for? If your in South America, maybe Jeff Fredette or Eric Gorr would sell you some porting specs. Eric has a two-stroke performance book available (Amazon or Barnes and Noble websites) that may have suggestions.
Good Luck,
Mark
KDX175
KDX200
XS850 Special