Its not your crankset, its not your chain(IMHO). 2 ways to go. Buy 6 Shimano or ACS freewheels and you'll maybe get two that won't clunk. Or just bite the bullet and buy a White Industries Eno and enjoy. In the past I did have some measure of success with Shimano and ACS freewheels by laying the bicycle on its side and spinning the wheel and dripping mass quantities of Phil Oil into the freewheel. But ENO is really the way to go.