i just picked up a pretty clean troy bilt tb320 for free because it wouldn't start. I pulled the very dirty air filter and the spark plug and confirmed it had spark. after reinstalling plug I sprayed starting fluid into the carbs throat and tried to start. it would spit a couple times and puff smoke through the carb and muffler, nothing happened. it would also make a noise similar to knocking with the plug in, but without the plug there was no noise at all. the guy i got it from said it ran fine last year and when he tried starting it up for the season it didn't run. im considering a lot of possibilities but i need to narrow down the root cause before I start buying parts to fix.