I just picked up a CC LT1046 with a CV23 Twin cylinder 23HP motor. At the time, it was only running on one cylinder. One of the spark plug wires was chewed in two by mice. Anyway, I don't know if the previous owner ran it much like that or not. But I changed the oil when I got it home. I ran it for about 20 minutes like that before I realized it was only running on one cylinder. So, I guess my question is: with the gas not getting ignited, does some of it push into the crank case during operation and should I change the oil again since I ran it that way for about 20 minutes before I put new coils and spark plug wires on it? If I do change the oil, can I keep the oil filter at least?