I have a 1999 YZ400F and I want to change the exhaust from the original FMF "Q" muffler to a FMF power core 4 Muffler. When I last had the carb worked on it was jetted perfectly to the FMF "Q" muffler. I was wondering if the jetting needs to be changed or will previous jetting work? I dont know what jetting is in there right now becuase my mechanic did not keep a record of what went in there when they fixed the carb Do i need to know and how would i find out???? Thanks for all of your help!!! Patrick M.