I keep waste-scrap plastic to melt then inject into all molds i intend to inject...with scrap plastic first so it doesn't matter if it yellows. If you're injecting remelts, you may be injecting not-quite-hot chunks that can plug the cavities. Also, similar to what Mr. Paul said, if your plastic isn't upto temp, you can get thick liquid plastic, and if this is present, they're cooler and can cool to too-cool-to-move much faster than to-temp plastic. I lube both injector o-rings with whatever i have close by, either stabilizer or scent/oil.