speedfight carb problems?

speedfight 100 dellorto phva 17.5 problems - bike starts well but as soon as you accelerate it starves of fuel but is happy to tick over indefinately- carried out usual tests, fuel delivery good cleaned carb jets etc all fine.replaced e choke then replaced again with manual choke makes no difference. funnily enough if you partially remove choke by 1mm the bike then runs much better , but the minute you reseat the choke full the problems starts again. have never come across a problem like this can anyone help as its unridable. many thanks
Tried advice given by Adam but no change to the running of the bike any chance the float could be causing the fuel starvation? (starts fine ticks over but starves of fuel on acceleration)

lee williams
September 2010