I have a 1979 610 bobcat. The fellow that use to own it, told me to never use the lever for high speed. I took his advice, never really thought much about it. At that time the thing just barely ran good enough to pull itself around the yard, So I never really investigated it. Recently I rebuilt the carb and put new gaskets on the manifold, so it will actually run without having to choke it all the time. Temptation got the best of me last week so I pressed on the handle and instantly the big drive pulley popped off. Was a bit of a struggle to get it back in place. Any Idea why this is happening?