Or - the reeds weren't designed for an 80cc kit. The larger piston will create more crankcase pressure.
You could try to find some Boyesen reeds. I measured and then took some pictures and sent the results to Boyesen, and thay matched them to a current product (this was for a Hobbit). Should work for you, too. They have fiberglass and carbon fiber, and one other type I don't recall.
Otherwise, you may need to buy reed material and make your own.