Craig, take the carb off and look from the lower end and make sure the spray bar opening is looking down at you. Remove the needle and make sure there's no filings there or obstructions in the spray bar. Then start the process from the beginning according to the instructions. If you suspect the muffler take it off and run it temporarily or try the stock muffler. Warn the neighbors. Slimline at one time sold the same muffler for the 60, 75 and 90. It was too restrictive for the 90.