Just correcting the valve lash adjustment corrects most of them.
I usually set them both at .005 inch (snug). If that does not correct the issue, then it will need to be opened up and the cam replaced. Aftermarket cams are junk right out of the box. Genuine B&S cams are often on back order.
Make sure you check the push rods for any bowing because that is a sign of the heads getting overheated due to dirty cooling fins. If any are bowed, replace them and be sure to remove the cooling tins and clean the fins out well.
