If you watch this video it will help as the rb and nova carbs are the same
http://vimeo.com/7595905
I used to run my ws7 on 20% nitro and 7mm and it was crazy fast and always got around 10 minutes. I sold it to a guy who raced truggies and he blitzed people with it even though it had done 12 gallons plus when I sold it and all on original bearings and rod. ACE ENGINE - they were never the same once they moved production to the far east....