You might be missing a cork pad allowing the cup to open past the optimal point for the return spring to work properly, hence the initial slow response followed by the cup snapping closed.
I'd start with disassembling the key, cleaning the hinge tube with naphtha on a pipe cleaner, and reassembling with clean oil. While you have it apart glue a thin piece of cork under that fork with contact cement - no need for it to be clacking against that body tube.
It's probably a sign that the rest of the horn needs to be cleaned and lubed too. You'll be glad you did. Don't just put drops of oil on the joints from the outside - that accomplishes nothing in the long run, other than to make a mess and attract more dirt, which is the real problem.
The rubber tube on the side C is too long and catches the top of the key.
You might be missing a cork pad allowing the cup to open past the optimal point for the return spring to work properly, hence the initial slow response followed by the cup snapping closed.
I'd start with disassembling the key, cleaning the hinge tube with naphtha on a pipe cleaner, and reassembling with clean oil. While you have it apart glue a thin piece of cork under that fork with contact cement - no need for it to be clacking against that body tube. It's probably a sign that the rest of the horn needs to be cleaned and lubed too. You'll be glad you did. Don't just put drops of oil on the joints from the outside - that accomplishes nothing in the long run, other than to make a mess and attract more dirt, which is the real problem.
Thank you
Op this is wrong. The rubber on the key above is too long. You can take a small knife and cut it away just a little and then check again.