Overview:   If your stock carbureted Subaru EA engine feels Gutless, slower than it used to be, and some times, it overreacts during acceleration and sounds louder while your subie runs like a bat out of hell, and the Hitachi Carburetor has a Vacuum Operated Secondary (high) Stage; I Bet that the Vacuum actuator that activates it, is failing.   Even with non failing vacuum activated secondaries; I've made Mechanical Conversions on those carburetors, always with Great Results. The Difference