Carefully scrape off the thicker stuff. Then use oven cleaner and 00000 steel wool to clean the rest. Do not use steel wool with any fewer zeros or it will scratch the chrome and or with any greater number of zeros as it will not clean the gunk off. Make sure to mask off all other parts of the bike so as to not get oven cleaner on them. Make sure to use gloves as the oven cleaner will quickly damage your skin.