Chris
I am by no means an expert with the Cub snow blowers but I would guess you may have sucked some snow into the air filter. I think I would keep it wide open the whole time you are using it rather than backing off. I also would not disengage the clutch just to back up. They way I look at it every time you engage it you are wearing it out. Sounds like you had it pretty well iced up. I'm sure others with more knowledge than me will chime in.
