I am using a GEBE Tanaka 40cc belt drive with a expansion chamber exhaust and a high performance carburetor and I am having trouble with rear blow outs. I was going 35mph for about 9 miles with throotle left to spare. The tires , tire liners, and slime tubes and wheel set are of decent quality. The trouble is at the valve stem, either the tire and tube is slipping causing this. Does anyone else have this problem while going at higer speeds? How can a person fix this issue? I am using about 60psi in both tires. The front tire seems to be doing ok at these speeds. Will I have to go to clincher style rims?