Here's some thoughts about this. Any chance the disc is in backwards and the center hub is rubbing on something? Can you look down in, press the clutch petal, and slide the disc back and forth? If all is good there, maybe try filling, or over filling, the transmission with the thickest oil you can get to make it "drag" more than the clutch. If it's worse now that you modified the disc you may need a new one and maybe just put a dry clutch in it and don't add oil.