I have an MS290 that is now out of warrenty. It has been a good saw, but I have been frusterated with the lack of power when tackling big wood. Today I modded the muffler in hope of correcting some of this. I know that I need to retune the carb, but am not sure where to start because I assume that the manual starting points will no longer be valid. Im I correct? Please help me get started.