Hi all, I just received a John Deere L120 with the Briggs 22hp engine. I got it for free and it has just over 500 hours on it. The mower runs but it just doesn't have any power. I changed the plugs on it and it seemed to help a bit but it's still lacking a lot of power. When you engage the blades, it just about dies but will stay running. Haven't had a lot of time to look at it and not really in a hurry but just trying to get some ideas on where to start to get this engine running good again. Thanks