As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DISCREPENCY: AIR TURN BACK FOR SMELL OF BURNING INSULATION ON ROTATION. NO FIRE INDICATIONS. ENGINE PARAMETERS NORMAL. REF TSM 05-50-00-810-831-A FOUND ODOR TO BE LAVEL "A" AND LIKLEY SOURCE TO BE "TYPE 2" #1 ENGINE. CORRECTIVE ACTION: PERFORMED LEVEL A DECONTAMINATION OF ECS PER AMM 21-00-00-615-802-A. NO REMAINING ODOR PRESENT. A/C OK TO CONTINUE.