5,000-6,000 sounds like the transition from needle to main jet. If it's good wide open, I would first try raising the needle one notch.

 

One thing at a time, I raised the needle one notch, I hate the expanding diaphragm by the way. Bike run strong between 5 and 6000, but the stutter moved up to between 6 and 7000. So I put the 132 main in. Problem solved, smooth strong power all through the range,, stutter is gone... I am very happy...one thing noted since installing the 340, max RPM is about 8500, it now gets there quick, real quick I imagine there would he more if I open her up more, Fmf etc.??

Ed