I have a Troy built rear tine tiller model 21c-65m1011. I think I purchased in 2008-2009. Used very little. Ran rough last year but was able to till whole garden. Left in elements since last year. Would not start this year. Carb was full of crud. Gas tank was trashed - rust, crud, etc. I replace gas tank, cleaned carb, cleaned fuel line and new fuel nipple / screen. Also, new spark plug. Starts first time every time and idles forever - although slight rough. When I put in gear tines and tires rotate fine - no change in engine speed or performance. The instant I lower the tines in the soil the engine dies. I can see governor arm push throttle open as it immediately dies. I then bought carb rebuild kit and did. Same results. Then I bought whole new carb and new air filter. Same results. Appear there is no fuel diaphragm or fuel pump. Seems like gravity fed. Pulled valve cover and blew out breather tube, it was clean. There is a slight pinch in the breather tube from going around housing. So, everything upstream from the carb (including carb) is new except the fuel line but I can see through it and seems perfectly clean - no dry rot etc. spark plug was gapped according to manual. Not sure what else to try. I did read some posts on gap on valves, I have not done anything there. A coworker suggested checking springs. 2 new springs - throttle and governor springs are in transit. The governor spring is completely rusted. The throttle perfectly clean. Thanks in advance for your help!