Hi!
The MVVS Q-500 has a 9mm carb not a 9,5mm carb.
I have run (competed in pylonracing ) several of these engines running 80/20 fuel (20% castor oil) and used either APC 9x6, 9x6,5 or 9x7 props.
Rossi 6 is the prefered glowplug running this fuel.
Hope this helps to get you started.
Regards!
Jan K
Airracing products
Swedish MVVS distributor
http://hem.passagen.se/airracing