I have one of those 170 models that I bought new in 2008 and it was running poorly. The spark arrestor screen in the exhaust would plug up. I cleaned it a couple times and finally just left it out. I also a few years ago put a chinesium carb on it that was about $20 or so off ebay. It worked fine with that. I have used those aftermarket kind of carbs on several of my mowers and snow throwers with good results.
Bill
Bill