Under the rear of the precleaner and at the front of the front chaffer sections, is an opening which allows air to spill from under the precleaner. This robs the sieves of air, and you may not be able to get enough air under the chaffer to open it wide enough to let your crop thru without trashing. This air also can blow across the top of the chaffer, pushing grain to the rear too quickly. Suggest you hang a piece of belting about 9" wide under the rear of the precleaner to keep this air in.