Here is the Musgrove with some changes I hope make it run better, I got a heavier fly wheel as the first one was only 260grams and seemed a bit light so I bought one made of Zermak which is 700 grams and was easy to machine. Timing is tricky with this engine so I found fitting a tube to the exhaust and holding it to your ear lets you hear the valve opening.
Geoff
https://youtu.be/5kgi8yf3xLU