There is a device called a Dial-A-Jet that works on some carbs, including the Mikuni CV on the XT225. I have not tried it yet, but everyone who has seems to like it. Don't know if it would work on the C70 or not.
I just found out about the TAT. I wonder if a properly modified XT225 would make it. Sure would like to try if I could find a way.
2002 Vulcan 750, 2013 Royal Enfield B5
2001 XT225, 2009 Genuine Stella
2012 Zuma 125, 1980 Puch moped