Make sure your gas key is tight on the bolt. I had an improperly staked one work loose years ago and it exhibited similar symptoms. You could be borderline on your gas to start with, and if you lose anything b/c of a loose key it can act undergassed.
It took a while to figure out, but snugging the the gas key fixed it, then I made sure it would never happen again lol.
It took a while to figure out, but snugging the the gas key fixed it, then I made sure it would never happen again lol.