That is your primer that adds additonal fuel to start the motor when cold. The "tire stem" thing is a preventative maintenance valve used when decarboning the motor with engine tuner.
Go to your local Evinude dealer and purchase a new primer cap, yours is cracked.
I believe it comes with a new gasket.
You will have to remove the red lever and install it in the new cap.

The red lever must be "in-line" with the body of the primer for automatic operation when the key is on and pushed in.
When the lever is 90 degrees to the body of the primer it is in the manual position.

If you have an operators guide it will provide information on the use of the primer for cold starting and maintenance.