gz 250 wont rev up

[22matt22]

i have a 2003 gz250 an when i got the bike it didnt run it sat up for a wile i cleaned the carb like 4 times then had it boild as they coaled it an it starts up i road it down the streat then killed it the next day i started it up an idels but its idled hight but when u give it a lilbit of thotel it will idel like it supost to but if u keep puling the thotel it dies i have checked the valves the petcock every thing is clean an right does any one know y on earth its doing this i just dont under stand it