What was found
ON TAKEOFF, DURING ROTATION WITH APU RUNNING & APU BLEEDS RUNNING, A BURNING ODOR IN THE COCKPIT WAS EXPERIENCED & QUICKLY DISSIPATED WITHIN 30 - 40 SECONDS. ODOR DID NOT REOCCUR REMAINDER OF FLIGHT. GROUND RAN APU SEVERAL TIMES, NO UNUSUAL ODORS NOTED, PERFORMED ENG RUNS WHILE APU ON WITH NO ODORS NOTED.