I looked at a picture of the felt filter in the manual, Aldo, and I can't believe it is meant to have oil on it. Now that you have it clean and dry, if you replace the spark plug as well, by the time it runs long enough and hard enough to burn the carbon out of the muffler, it should be as clean-running as a new one.
Thanks for reporting the outcome - I'll close this thread. If anyone needs to post to it, just PM a moderator.
