I have not used a machine that has cams, but try this: Oil and clean the machine, just in case, check the feed dogs, make sure they are up. When you clean the machine, make sure you oil in the faceplate area, too. Good luck! Let us know how you make out.
PS, if you are willing to go with a used machine, check out yard sales and thrift stores. I got a great machine in a walnut cabinet a couple of weeks ago for $.79. Lookee there, money was NO problem that day.