04 Honda Foreman 450 Wont Start

I feel like you guys read a thousand of these and im hoping someone can help me out! First post on this forum as Ive joined to try and get my atv running. I have a 2004 Foreman TRX450 4x4 ES that i recently purchased, i did a full carb cleaning and cleaned my spark plug up and with new gas and the help of some starter fluid i got her going, for a few weeks anyways! The bike was left at my parents where a little brother was riding it daily just to flush everything out and keep things moving and then one day it just quit, they said it backfired once or twice when trying to crank and then just would turn over and over. So i pulled the carb again, cleaned and replaced and then replaced spark plug. THought maybe my needle and seat was shot so bought a new carb, installed and still wont crank! The oil level was a tad low so ive added some thinking maybe there was an oil sensor and no luck! I have spark and I have gas flow but still wont crank! Any help is greatly appreciated! Thanks