[EastCoast]

I have a new to me RZT -S 46, 2016 model. I've always been a Kawi guy but this unit came up at a good deal. I'm trying to diagnose why the engine is running rough. Only one side runs rough. The other side is fine, thus ruling out fuel, air or carb issues. I have replaced the plug and have Amazon'd a new magneto. The problem seems to get slightly worse once the engine warms up. I do hear the occasional backfire, infrequent however. The unit only has 300 hours on it and is in very good shape. Power is low. The mower had a head gasket replaced before my time. The side that is rough also leaks a little at the valve cover. Any thoughts?