I have a 2nd series '55 and every time I remove the gas cap it makes a sound like I'm relieving a vacuum. I always thought it was normal, but now it keeps stalling and will only idle. The fuel filter is clean. It will idle perfect, but as soon as I hit the gas it stumbles. If I shut it off for a minute or two it's ok for a little while. Should it actually have a vented gas cap on it? It has always made that noise and I have driven it 2 hours at a crack with no troubles so I don't know why all of a sudden I'm having trouble.
Help please!
