The stock shims set a factory preload on the spring so that you get X advance at X case pressure.
When I have the spacer in in the summer, my idle RPM drops and engine wanders (can't think of any better way to describe it) at idle. Runs great otherwise. In the winter it's a real bugger to start, so I take it out.
My suspicion is I loose that spring preload with the spacer. So instead of the spring tension holding the timing piston against the bottom stop, it floats when case pressure is low like at idle. When the KSB is activated (cold weather starts), it gives me too much timing for a cold engine.

 

Never had that issue with mine worked great I bumped it up alittle from stock to. I've even hot wired the ksb and she just rattles alot.

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So I just relized I put the old spacer on top of the new thick spacer on top of the spring. I did not use the shim WHOOPS!!!! Should not hurt anything. I hope!!!!