First thing, get the rubber out of your engine mounts. That isn't helping anything and can contribute to your problems.
Second where do you have the tensioner mounted and how tight are you keeping the chain. You'll want 1/2 to 3/4" of slack. More or less can cause chain problems.
Chain alignment and tension is critical. Roller chains must ride straight and true between sprockets with absolutely no lateral misalignment.
You might also check the teeth of the engine drive sprocket and see if there are rough spots on the ends that engage the chain. We always suggest to smooth the teeth of both the drive and driven sprocket to make chain engagement smoother.
A photo of the installed chain/tensioner/rear wheel might help us give more suggestions.
Tom