gilera dna 50 when running loses all power afer about 15 mins?

If the bike has had a new performance pipe fitted ,it may be jetted to rich,so would run fine till it has warmed up,usually 15mins.with out knowing the history of the bike its hard to say.also check the oil pump is working ok as i seem to remember the cable can stick where it joins the throttle cable

mikc
April 2010