Pulling shims out of an engine can really help the performance as well as steady out an erratic idle. It is VERY important that after pulling shims out you remove the glow plug after a run and check the top of your piston. If you see any tiny pit marks on the top of the piston you need to put that shim back, even if that's the best your engine has ever ran you need to put it back. That is a sure sign of pre-detonation and continued use like that will eventually kill your engine.