Son starting complaining that QT50 was getting hard to start and wouldn't restart after stopping. Wife said she noticed some smoke. I'd never changed crank seals on this one, so I did. First attempt after changing seals, it cranked perfectly, rode for about 5 minutes, it bogged and died. Watch the video. Spark is great, compression is fine, clear fuel line with good flow, spotless carb. What's the deal with this thing?