you are using it wrong.
Weightnorm has to be registered in the constructor, on a module.
self.conv1(x) returns a Variable.
Rather, you need to do something like this (where you defined self.conv1)
self.conv1 = nn.utils.weight_norm(nn.Conv2d(...), name='weight')

Read the docs (especially the example in the docs) for more details: http://pytorch.org/docs/master/nn.html#torch.nn.utils.weight_norm 456