I have an x520 w/48" deck that I have just taken out of winter storage. I drained the fuel and replaced the filter, drained the oil and replaced the filter and replaced the blades. Yesterday it started right up but ran rough and stalled as soon as I released the brake. Eventually, it would run under load and I was able to mow but it started to stall and backfire. I let it cool overnight and added some oil. Again it started up but would not run under load. I pulled both plugs. They were completely clean with no oxidation or other buildup at all but it does appear that there is motor oil on the threads.
