Having fitted carb tune up kit it still won't rev right up the rev range. I thought that might sort it, it's fitted with electric ignition from ty trials which may have been altered 'I leant the bike to a friend' so advice on setting that would perhaps help as well.

ANY help appreciated 

check the reed valve , I had same issue , reed valves were nackered .

 

Also check fuel filter, happened to me and eventually realised fuel filter in tank full of crud, enough fuel getting through to ride but wouldn’t rev