CBR250 engine is a good choice. Is there a California spec version or are they all? The reason I ask is that the California version of many of the older fuel injected bikes had an O2 sensor, meaning closed loop, meaning more efficiency.
What I would do is go to bikebandit.com, look up the parts schematic for the bike in question, and see if it has an O2 sensor at all. If it does, then BAM!...that's a good candidate.
Example...check out this CBR250 breakdown. Item #11 is the O2 sensor. BAM!
2011 Honda CBR250R Parts, 2011 Honda CBR250R OEM Parts - BikeBandit.com