I had a similar problem with a 3W 100 twin. The reeds looked physically fine (no cracks, curls, splits). I replaced the entire ignition and carburetor. I put a gas tank on the ground and ran the fuel directly to the carb. I start the engine, then pick up the fuselage (wings removed) and roll the fuselage sideways and upside down. The engine drops about 500 rpm or more (Sounds like it goes rich). I sold the engine.