[WSSix]

Did you have the new flywheel balanced matched to the old one? You can't just replaced an external balanced flywheel with another external balanced unit. They aren't necessarily counter weighted the same.

If you didn't do this, you need to take the old flywheel and clutch pressure plate along with the new flywheel and clutch pressure plate to a machine shop and tell them what you're trying to do. Don't ever assume a clutch pressure plate is zero balanced out of the box. Always include it when doing any balancing work.