Thats some great info thanks guys,it all make sense,the same way acetylene needs oxygen to burn hot.Ill just try making/replacing the exhaust gaskets for now and sealing them up,maybe then Ill try lifting the circlip one notch to see if it revs clean.Thanks so much.Ill report back tomorrow after the test ride.
I wish it was easier to post pics on this forum,we have an awesome natural terrain MX track and the old bikes just look great running round there.Ill be taking my SLR camera out there tomorrow.