how do i fix my ryobi rbc30sesa strimmer?

i have ryobi petrol strimmer and it will only start when cold but will not run when i put the choke off. i have replaced the carbuerrator, the heat dam as this had slight crack and all revellant gaskets and fuel pipes. there are a good spark at the spark plug. cut it be taking in air around sealant on the fuel tank.