I guess I'm part of the kstar no low end club. It's better when cold but when it warms up I too lose some low end until around 20mph. Then it rips.
Here's my setup
Puch Korado e50
Kstar 50 w/ high comp. head (not port matched)
Dellorto 15.15 with a 70 jet
Currently has biturbo pipe, but had tecno boss pipe. both pipes had bad low end.
Plug chop shows a light to med brown