i suggest you arm yourself or get some mates to help you fight him. he has a huge advantage over you if you take him on in a fight. the bigger they are the harder they hit. your punches are unlikely to hurt him due to him being cushioned by his body fat.
the way for a smaller person to take on a bigger opponent is with a good sneaky surprise attack. if he lands a good hit on you, you are knocked out. there is a good reason light weight boxers never take on heavy weights.
anyway why are you fighting this guy? what is the fight over? i hope the fight is worth it. you will either get hurt or he gets hurt and either or both of you will be in trouble with the police.