Happy birthday Gareth.
RE the Yammy Fizz. I had a Suzuki ER50 (30mph jobby) and took the 15/2 front sprocket from an FS1E to replace the smaller one on my bike which made it go an indicated 38-40mph on the flat but it died as soon as it saw a hill. Considering the ER50 was an attempt at a trails bike it seemed to defeat the object but it still had the edge on most of the other restricted bikes.