The gz come from factory tune for emitions and that make the engine to run hot and lost power.
you can impruve the cruse speed with som tuning
i have
16 t
140 main jet
2.5 turns on the pilot
unrestricted air cleaner
cruse speed at 70-75mi an with good conditions 80 mi
with out the carburator mods do not go over 60 mi
mode air filter ( do not mode the filter without change the main jet )
http://s18.postimg.org/sneq60k8n/IMG_20 ... 110644.jpg
check this post to
viewtopic.php?f=7&t=6170