I just purchased a used 5.5 hp 2 stage 4 cycle snow thrower. It doesn't have a brand name. It seemed to be working fine when I purchased it. However, we just had a big snow and when I went to use it, it won't shift gears. It has 5 forward and 2 reverse, but it seems to be stuck in 5th gear no matter where I put the gear shift. Also, when I move the switch from choke to run the snow thrower starts to back fire. I'm going to call the person I purchased it from tomorrow morning, but wanted to see if anyone had any ideas? Thanks!