I bought a brand new 128CD and it sucks. The motor works fine but the moment i start cutting and the strings get resistance, they stop spinning. Spinner works fine when cutting air, but not when cutting grass. I have confirmed that its attached properly, secured tight, and lubed up. Again, it spins at full blast/power when not cutting, but when you put it to the grass, it slows down. The engine revs up, but it doesnt spin the trimmer. Whats the problem here?