Hi, I'm usually over at the model section of HobbyTalk, but was relieved to see this section here.

First, I know very very little about engines, so....

My B&S mower engine from approx '89-90 is sputtering after it's started for a few minutes. It has a "pulsing" idle, then after cutting for a few minutes it starts to sputter pretty bad then sometimes stalls. It doesn't smoke, and the carb was rebuilt last year. The problem was less pronounced at the tail end of last season. I thought I had some bad gas, removed it, added fresh gas, cleaned the carb with some gumout spray carb cleaner, changed the oil, airfilter, spark plug gapped to manual spec's.

My bro in law suggests it may be the magneto. Anyone have any suggestions?

I need to fix it quickly, because my lawn is high except for the 2 stripes I cut before the mower started acting up bad.

Thanks,
Brian

ok, for when you first start it up, it runs perfect right? then all of a sudden it starts popping and puffing? yeah it could be a failing coil under heat which does happen. now if it starts and backfires alot, could be a partially sheared key, though i'm leaning towards the mag.