If your mower's engine pops, it could be for a number of reasons. The most common reason is that the air filter is dirty or clogged. A dirty air filter restricts air flow to the engine, causing it to run lean and eventually pop. Another possible reason is that the spark plug is fouled or damaged. This can happen if the mower's fuel mix is off, or if the spark plug isn't getting enough Spark. A damaged or fouled spark plug will cause the engine to run lean and eventually pop. If your mower keeps popping, check the air filter and spark plug first. If they're both in good condition, then you may need to adjust the carburetor. An easy way to do this is to take the mower to a professional for tune-up.