FLL, I wonder if your original problem with this snow blower involved the carb choke? It sounds like it may have been running a little too rich and the excess gas was collecting in the muffler. I presume you had to choke it to do a cold start but I wonder if you didn't get the choke fully open once you began using the machine? Just my .02 cents.
Here's another .02 cents; next time, buy an Ariens Sno-Thro! I've been using them for over 40 yrs and I've never had a complaint. THE BEST snow blower ever and it's made in America!
Also, whatever you buy, don't buy from Lowe's or Home Depot, buy from a real small equipment dealer. It seems like Lowe's and HD sell a lower grade variation of the brand names we're all familiar with.