Thanks for the very helpful insights.
The spring in my 3435 is the one that was there when received. I simply assumed it was original, as I got it from an in-law relative who was the original owner (or so I thought). Pretty sure my spring is touching the spindle, and I can see where that could cause it to short out.
I'll try un-wrapping the cord and use a half loop with a shorter spring and see what happens.