I have a problem with the FC150V engine (6.0) on this mower. The speed wavers greatly with it, UP AND DOWN particularly when not under load. I have cleaned out the carburetor with a complete disassembly, but still, it does this. Does anyone have experience with this problem on a Kawasaki engine? If this were a vacuum leak, it seems like it would do this regardless of whether it was under a load. Thanks.