I just pulled out my cub cadet from storage after sitting for a couple of years. I started it up and a cloud of smoke shot out and backfired. I noticed there was gas mixed with the oil, so I drained my oil and replaced my spark plug, air filter, fuel filter, oil filter, and put new oil in it. I also cleaned the carburetor out. When it runs on low idle it sounds good but when I full throttle it starts spitting and sputtering and starts back firing. Is it time for a new mower?