It is easy to kill-off an historic race class if the class is not designed around engine capacity and type of bike. A friend of mine had a 250cc 1950s Montesa two-stroke which was eligible to race in 350cc period 3 class against the 350 Manx Nortons etc. The Montesa used to win easily. When I pointed out to my friend the difference in racing costs, he then applied for another log book and moved his bike into the next class which was for 1960s bikes. Which I thought was pretty decent of him. He still won races but his wins were more appropriate. One of the things which commonly happens, is the guys cheat on capacity - 'big is better'. So what you get in Period four are big methanol fuelled four cylinder bikes doing point and squirt racing. There are very few two-strokes in Period 5 (1970s) racing, the cost of racing a TZ against big four cylinder bikes is not justified by the type of racing. If I do historic racing, I race in Period 4 (1960s). The front of the field is 1100cc methanol-fuelled CB750s. So it is rare for a 750cc Triumph or Norton to be there. There are a few two-strokes, but I think the guys don't really know how to make them go fast. They should be able to easily beat my Seeley 850, but don't.