YZ250F is back firing when let off the throttle. Would hot start sticking cause this problem?

No buddy your mixture is too rich which means to much fuel is going in and not enough being burnt so the access fuel goes in the exhaust and then gets burnt in the exhaust which is a explosion so you get a back fire to cure this problem you need to screw the mixture screw in which is located on the carb a picture below will demonstrate turn this screw 1/4 of a turns in this will decrease the amount of fuel going in and stop backfiring good luck bud