I’ve been having a problem with my Evo kit also, I own a junior kart that just received the upgrade. To my surprise when I went out for practice the kart would not exceed 10,000 RPM’s. I’ve changed about 8 jets all without results and the motor pops until it hits 10,000, then the motor bogs down rendering my straight line speed close to none. The fuel pump, clutch and more internals have been changed with no change at all. I am now contemplating on whether I should send my kit back of put the older carb on.