The handlebars are barely movable when the parts "GEAR1" and "GEAR2" are unsuppressed but otherwise perfectly movable when they are suppressed. Are they incorrectly attached to the assembly?
To test the constraints of individual components you can disable the assembly constraint rather than suppressing the component. This should allow you to determine if a specific constraint is problematic.
You could also use the DOF functionality in mechanism to study how many degrees are still free.
it is in the placement tab under component placement in assembly mode.
I suspect that is in the case of using a predefined connection joint (i.e. pin, planar etc.). You can disable the set as a debugging exercise when reviewing mechanism connections.