What Causes Gas to Get in Oil on a Small Engine?

Gas mixes into the oil when fuel leaks past its normal path into the crankcase. The most common cause is a stuck or leaking carburetor float needle, which lets fuel keep flowing even when the engine is off. Other causes include a worn or cracked carburetor float, a bad fuel pump diaphragm, worn piston rings, faulty valve seals, or flooding from excessive choke use and hard starting. A stuck carburetor inlet needle is usually the main culprit. If you notice a strong gas smell in the oil or a rising oil level, fix it quickly to avoid engine damage.