Regarding the race series, Regs are on the Fab Racing website, moto-team pages.
We have a huge variety of machinery racing, from 50cc watercooled minarelli engines (17-20 rwBHP), down to 125 cg engined specials.
A couple of teams have used the standard cg frame with varying degrees of success, but Dans has got about 14BHP (from standard 9bhp), with derbi senda USD supermoto forks.
My machine last year was an Aprilia RS50 with a heavily modded cg125 motor.
Am in harrogate if you fancy a jolly over, plenty of honda 125 engines in bits to see.....
The most effective way of turning petrol into noise without the side-effect of horsepower