I have an MTD 2 stage snowblower. I recently had to replace the worm gear but now it works fine. This last time I started it it was really loud compared to what it normally is. Seemed to get even louder as I turned down the throttle. Everything still worked fine but after 5 minutes of using it it started spitting black smoke and I could tell it was about to die so I just shut it off. The gas is not old. What on earth could be happening? Worked perfectly fine last time I used it and now it doesn't? Thanks

Black smoke is usually indicative of too much gas. Choke could be stuck, float possibly stuck. First focus on the carburetor and make sure everything is properly aligned and functioning.