Open up the outlet of the muffler . It generally 3/8" or less depending on the saw . Open it to 3/4" . Make sure you richer your mixture ! Go to arboristsite.com ,and do a search . Or, go into the chainsaw forum and ask how . Be ready to defend your choice of chainsaw brand ..... They are a hard bunch !For the life of me I cant find how to do the muffler mod.