Just for yourself, that bike is NOT fuel injected. Its a standard carb, butterfly, vacuum operated throttle slide...
Is the issue the engine noise or the slight hesitation with the throttle? (knocking I guess?).
The hesitation /roughness can very well be from a dirty carb, poor fuel.
There should be a drain screw on the bottom of the float bowl. Remove that and catch the fuel that
comes out in a clean container. Watch for any crap that comes out.
If the main / idle jets are partially clogged, you might get by with using a very good fuel system cleaner as the engine
stills runs decent. If not, R&Ring the carb, float bowl and then inspecting / cleaning the two jets would be in order. Just
spraying with carb cleaner don't count either. If you can't see light thru the jets, their NOT clean...
Lastly, how old is the spark plug?
If it's old, worn, gap wide with wear, will hamper overall performance...
