Re: When I cover bottom valve cap and press valve, valve comes back slowly. What is w A fairly quick DIY fix would be to scrub each piston for about 5 minutes each with 200 grit emery cloth. If done properly, each piston should rebound quickly even with the bottom cap sealed. A bastard file would be even quicker. The horn will also pretty much sound like a vivuzeala, or whatever it is they are called.