I agree with Robert on this. When a fresh carb is running properly and suddenly has issues its almost always a fuel contamination issue. The only other two carb related issues that affect performance on a new carb are a bad float (even brand new ones occasionally have tiny pin holes causing slow leaks). A bad needle and seat, or a bad acc. Pump (todays fuel is hell on both). Based on your description Id go with fuel contamination as my first guess follwed by some non carb issue like ignition.