Long story short my grandparents Craftsman riding mower with a Kohler 17 wouldnt start. I replaced the plug, checked for spark, drained the gas and refilled it, replaced the battery, then I went to check the oil and it was full of gas. I drained it all out, flushed it with a quart, put 2 quarts in, put oil into the cylinder with the plug out and cranked it(good compression). Now it cranks, backfires when I adjust the throttle. I still have spark and its getting gas. I also tried starting fluid to no avail. Thanks in advance for any info.