Help With Mini Dirt Bike

Hi I have a true 49cc mini dirt bike, but i have a problem, my friends go faster than me but they only have 47cc bikes, could someone please reccomend some upgrades to keep up with them?

P.S. i weigh 80kg and they weigh between 65 - 70kgs

Thanks

Toby

47 and 49 both same thing ur 49 not even 49 lol :P they both same engins? do u have like faster excelleration? If u do maybe like ur gearing causing ur top to be lower.. you should try lightening ur fly wheel good cheap mod :P he could be winning just cause he lighter..