My wife has a small clock, of sentimental value only, which has a spring with a weight on the bottom which oscillates vertically to operate the escapement. It runs for a couple of seconds but the movement that the spring exerts on the escapement quickly decays to a point that the escapement no longer operates because the claws do not move far enough to release one tooth at a time. I presume the escapement is not providing enough "driving force" to keep the spring oscillating.
The clock used to work perfectly, but has been in storage for several years because we couldn't find a key to wind it until recently.
I can't see anything that looks obviously bent or out of place. The main spring is fully wound. The coils of the "pendulum spring" are roughly evenly spaced when the spring is extended - one coil of the spring is not more stretched than another. The spring is securely attached at the top, so it can't have rotated to move the peg onto the wrong turn of the spring, which would cause the escapement claws to be unbalanced: it takes about the same amount of movement of arm1 either side of its neutral position to release either the upper or lower claw.
If the clock is placed face down so there is no load on the spring, the spring can be manipulated so the escapement oscillates very rapidly and the gears turn, which proves that the mainspring is driving the escapement and there isn't excessive bearing friction.
Any suggestions?