Automatic Cactus Farm problem

So me and my friends made a cactus farm where it feeds Bamboo as fuel into hoppers and furnaces, where the Cactus is instead smelt for EXP. The issue is, when the minecart runs over the cactus hoppers to feed them into the furnace, it keeps on filling the first few hoppers and instead 3-4 of the last furnaces are empty. Is there a way to counter it from filling up the first couple hoppers?