2008 Brute force feels like it's limping at 5mph
 

It takes several tries to start the atv and a few sputters but when we put it on the road to drive it feels like it's limping like a hurt person. But when we speed up, it goes away. Also, we don't feel it when driving on grass.
What could it be?

bad gas?

Could be clogged fuel filter or injectors. 2008 was the first year of efi on the 750. Though it wasn't specified whether it was a 750 or 650. The 650 still had the dual carb setup. Those dual carbs were a pain to deal with.