250cc Four stroke single wont rev

[Fms]

Any ideas its fine upto 5000rpm then wont really pull anymore. It pops and bangs ferociously on over run as well. I had the Carb apart and cleaned the jets but its stil rubbish. Im guessing its an air leak but where do i start? It has an automatic decompression that seems to be whirring constantly.

[YEN_POWELL]

Any ideas its fine upto 5000rpm then wont really pull anymore. It pops and bangs ferociously on over run as well. I had the Carb apart and cleaned the jets but its stil rubbish. Im guessing its an air leak but where do i start? It has an automatic decompression that seems to be whirring constantly.Tha auto decompressor can be adjusted incorrectly and it acts upon one of the valves. Do the valve clearances exactly as per the manual, especially with reference to the decompressor adjustment.

Also check the exhaust for leaks as these make the bike pop and bang when decellerating. I'm assuming its all standard exhaust, airbox and airfilter, as any of these being changed will need the main jet altering to make it run properly at higher revs.

[Fms]

Everything is standard yes. The exhaust looks in good condition i can see any holes. Its certainly not blowing. Do they have a condenser in the points?