I think I might have an engine problem... :(

Sounds like a running issue as others said. It's pretty much all been covered - drain the oil into a squeaky clean container, change filter, run the drained oil through a paint filter. Some "stuff" in the oil would be normal but chunks a paint filter will catch are signs of issues. Cut the filter open by hand or using a large cutter that doesn't produce chips. See what's in there. I would change the carb to a known good one. Anything 600cfm and up would do - you're only looking to remove the carb as a problem. Get the engine warmed up. Look up the tuning process. Research. Talk to Brian on some tuning ideas...