The more weight you have to lose, the easier and more of it you can expect to shed. So what do you weigh? On average, you could expect 1-3 lbs of fat loss per week. You could certainly lose more, but I wouldn't recommend. Aside from water weight, you would be catabolizing muscle which isn't the wisest thing to do.
Would cutting down on portion size work, you ask. It probably would for starters. Weight loss is dependent on energy balance. Calories are energy. If you eat more energy than your body requires, you will store the excess, read, get fat.
So, if you eat les of what you have been, sure, weight loss is possible.
I suggest counting calories though, since this way, you will know for sure which direction you are heading in. You could use something like
You say you eat primarily carbs. The funny thing is this: There is no such thing as an essential carbohydrate, only essential proteins and fats exist. Meaning, we don't even need carbs to function. That said, your diet surely needs some tweaking.