Check diameter of piston in M/C. some were 1/2", and some were 9/16". May "feel" different to your old one. But, if its still spongy, there is air in the system. No brake fluids are compressible, so the spongey has to be air. Sorry, I know that doesn't help. Get a bud to help you with bleeding, its easier if someone pumps, and fills up the M/c, and the other fella does the bleed nipple thing.