how to fix mccullock 38cc 18in chainsaw, model ms1838av?

sometimes its easy to start seems once its warmed up its hard to start, the carb zama has been rebuilt, new spk.plug,filters ect. has blue spark,good compression. after i let it run for 10min. at half throttle and shut it off, i notice the fuel was still being pumped into the carb from the tank and not running???? im at a lost, any help