i mow my grandfathers lawn for him because he's in a nursing home. i was mowing with his murray rear engine mower, and i heard a weird noise. i cant describe what it sounded like, but i know it came from the engine. right after i heard the noise, it started popping very loudly. fire and smoke was coming out of the muffler. i checked it a few days ago, and it still does it. thats why i say briggs engines are better than tecumsehs, we have not had a problem like this with any B&S engines before. im guessing, is it an internal engine problem, or a carb problem?