File size jumps from 5mb to 134mb somehow ??

Hi, i have asked this same thing a long time ago, but the thing happened again and im pretty annoyed because i just simply dont know why this happens. Simply by telling, stuff rotates around (usually exactly 90/180 degrees) and some things might scale huge(like 10x they should be). The file is just a simple car model for Assetto Corsa so it shouldnt be more than 8mb for the model(.fbx). I would put photo but i already deleted the ruined files i had and i will start over, but would be fun to know why this keeps happening on almost every project i have done. And before someone asks here is somekind of list what i have done to this file which is originally someone elses but i like to modify them for my own needs and mind set: Deleted parts of wheel arches?, widened fender flares, new set of wheels, new set of brakes, added more to the roll cage. might be some litle stuff more but i will add here if i remember. I also occassionally use 3ds max for setting the model to meters etc.