John deere 316 lawn mower

Starts and drives really well hydraulic lift for the deck works great. The deck itself is in great shape, but it is low on power and bogs down. Seems like only one cylinder is making power. Might be fixable if youre familiar with these Onan's. I was going to swap in a predator 670 but have too many projects so seeing if anyone wants to buy it as is. Will also need a battery. I have the grille for it in the shed.