Sporadic Clock Signals from Momentary Switch
All mechanical switches have the potential to bounce, and most do at least some of the time. 

That's exactly what is happening. You need to add a debounce circuit. The easiest way is something like this: 







simulate this circuit &ndash; Schematic created using CircuitLab

The RC slows the switch transition down, and the Schmitt trigger gate cleans it up so there is only one transition each way, thanks to the hysteresis.