Over an hour ago, I went to the Chevron to gets some gas for the lawnmower. Came back, filled it up. Started it and worked on the lawn for about 15-20 minutes. It was starting to get dark outside too. Still enough light to see, but enough darkness to see a couple sparks spit outta the muffler. Concerned about a fire hazard, I immediatly slid the lever to the OFF position and the engine took a while to shut off. (probably dieseling) I did put Chevron with Techron in it. Could it be that the Techron was cleaning some of the shit outta there and spitting the burning debris outta the muffer? This lawn mower is pretty old. It's gotta be at least 15-20 years old. It does seem to run very good. But what could the sparks coming outta the muffler mean? Maybe it's time for me to take the head off and clean the valves and shit.