I have a used Homelite UT20042a 2cyc trimmer. I put in a new recoil cord which now works fine and pulls easy (normal I think) when the spark plug is OUT. When the plug is IN it becomes ridiculously hard to pull the cord. I removed muffler and exhaust components, but the cord still pulls (and turns over) extremely hard. This is bad for my shoulder, and I wonder what else might cause this problem ... before I give up on this trimmer. Thanks !