Have you checked your deck housing to see that it is not coated with grass. Could be limiting air flow and circulation. I use a spray on product call 'Mow Deck'. I clean my housing and spray this stuff on. Helps keep buildup off. I get it from a site www.cheapmowerparts.com or call 888-227-5940. A can runs about 7-8.00.
I would check belts and idler pulley tension. Since you bought it used, may not have right belts on it.