You might want to pull the tension off and clean it up then re-assemble. You will need to have a manual or some good pics to help you get it back together.
http://www.tfsr.org/publications/tec...achine_manual/ or utonopedia.org/crafts-and-technology/fabric-and-dyes/basic-sewing-machine-repair
If there is a lot of crud in there dental floss won't make a lick of difference. I pull them, clean and then re-assemble just to be sure everything works.
Kerosene works but it is not necessary to soak a machine in the stuff. A lot of times sm oil does the job. Some times you will need something stronger but why get out big guns if you don't need to.