I seem to remember that you must be firm with the Kiev shutter, too gentle and the mechanism does not fire in the correct order, but it does not mean you have to jab at it, but make sure the pressure follows through, without stopping. It may need a bit of dummy use to check it is not grease bound etc.
I have one of the 250's too. The lens and camera combo has hurt my left hand. I hold and shoot with my left hand and wind and focus with my right. I've constructed a Salyut to M42 adaptor so I can use this beast on my Pentax or Sony. Results to follow.