QuestionI have a Craftsman walk behind mower - model no. 917.388561. For the last several weeks it has been running rough and even stalls. I changed the oil, cleaned the carb and fuel lines and replaced the spark plug (which was very carboned up). Also, siphoned out old gas and added all new. It ran great for about an hour then resumed the same problem. Today I replaced the spark plug again, put a little mower oil into the spark plug hole and cranked it to lube the cylinder, replaced the air filter (even though it was fairly clean) and added stabilizer to the gas tank. I started it up and let it run for about five minutes to let the stabilizer work through. Still rough. Removed the new spark plug and it was completely carboned up. I cleaned it and put it back in. Ran for a few minutes (it ran slightly better). Again removed plug and it was black but more cleanable. Did this once more. Same results. Put tiny bit of stabilizer directly into the carb, hit the primer a few times and let it sit for a few minutes, then restarted. Better but still not right. At this point I quit for the night. Sure hope you can help me. I don't understand how a plug can be so fouled in just a few minutes of running. Thanks.
Answer Looking at the mower on Sear's website, it shows it having a
different engine than the one you are describing. So if you could get back to me with the engine's model numbers, I can be more helpful.
Either the carb is running too rich, or oil is getting into the cumbustion chamber. Look and make sure that the choke is fully opening in the run position. If it is an OHV, there is a possibility of a leaky head gasket, but it sounds more like a rich
running carb.
When cleaning out the carb, did you have it all apart and blow it with an air gun? Some carbs have a jet that can be lost that way, and the carb would run too rich.
Let me know what model number you have, because I am curious.
