Hi there Annie If these are new pianos, and the action is reasonably well regulated then my first guess is always too strong jack return springs and / or too strong damper springs. Both tend to leave the jack top just a tad too close to the butt. A clue that these springs are involved is that the double strike goes away if you insure a very firm bottoming of the key stroke. On older instruments, lots of things can come into play. Alan delt with most of that nicely. Tho I would add that the jack stop rail on occasion can also need adjustment. Cheers RicB Annie Grieshop wrote: I had two tuning jobs yesterday that involved relatively new Yamaha verticals - an M500 and an M450. Both have very jumpy jacks (or, at least, that's my analysis of why they're tending to double-strike, even when well-regulated), and I'm wondering why. Both have plastic jacks and synthetic buckskin. The M500 had been treated with something that looked graphite-like and was less jumpy than the M450, which leads me to believe that the proper lubricant (or other treatment) might solve the problem. I would very much appreciate any suggestions as to how to proceed. Thanks!
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