I have one for you! If my 400E sits for a couple weeks, it runs great for the first 10 minutes or so, then starts missing, backfiring, stumbling. After you run it this way for a bit and shut it off, let it sit for hours to cool off, it is fine from that point on. Start it the next day and run it, it is fine. Only after sitting for a couple weeks will it do it again. I thought maybe the gas cap wasn't venting right causing it to build up a vacuum in the tank, but that wasn't it. Anyone have any ideas, or experienced this?

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