Senior VR Member
Join Date: Sep 2012
Thanked 97 Times in 80 Posts
What year bike? Is the tank vented? If the tank is vented, i.e. can get air to compensate for the fuel being pumped out by the fuel pump, you don't need a vented cap. If however, the tank is sealed, you need a vented cap to bring air in.
2008 Boulevard C50 - Among other things