hi,
the 4013 is a cmos device, that is, the impedance of an input pin is very high.
From your diagram pin 11, clk2 input, is floating, any electrical noise will be
picked up on this pin and could switch the device into an unexpected state.
Connect a 4k7 from pin 11 to the 0v line, in parallel with the 4k7 add a
0.22mf capacitor and from your push switch put a 470R resistor in series with
the switch and pin 11. [ a simple debounce r/c filter] . If your switch is of
a poor quality you may have to increase the 0.22mF to say 1mF.
Place these extra components as close as possible to the 4013. keep the
wires as short as possible.
This type of 4013/cct is very noise prone. Have a look at the one posted
recently that uses two invertors in series, its a proven method.
If you need a sketch let me know
Important: never leave cmos device input pins floating, your circuits will do strange
things ie; work one minute not the next. Also they could be damage by ESD
electro static discharge from you or your equipment.
Tie them directly to 0v or to +5v via a 10K resistor.
Regards
EricG