Engine (on a Murray mower) starts and runs, but smokes and runs very rough. I think the fuel mixture is too rich because the engine runs perfectly just before it runs out of gas in the tank, but I can't find any way to adjust carb. I have changed spark plug, the gas vent cap hole is clear, and the engine runs the same when the air cleaner is off. Any suggestions on what the problem might be and how to fix it would be appreciated. This mower is a few years old, but has not been used much. It used to run fine. I don't know if it is related to the current problem, but the problem seemed to start right after an oil change. The engine codes are: Model: 10A902 Type: 2291 B1 Code 99102554 Thanks for any help anyone can provide.