You have to adjust the throttle linkage. The trannies are not like a car where you can take it outta gear it's always in gear, but by adjusting the throttle linkage you can get it to a point where it'll stay still but still be running. If you did nothing to it perhaps you melted the clutch show to the housing and shaft? Is it running fine when you get it going? I'm hoping you did not run it too lean.