The Stovebolt Site Forums The Shop Area Engine Shop Should gas cap be vented???

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!

yes the cap should be a vented one.As the fuel pump removes fuel from the tank, an equal amount of air must replace it,or a vacuum is created.I think the amount of fuel in the tank would affect the drivability.The fuller the tank,the sooner a vacuum is created

An addendum to BC52's post. One possible reason you are now having difficulty where you didn't in the past could be that you had a strong enough fuel pump to pull enough air into the tank past the unvented cap to allow the engine to run & now the pump is getting weaker to the point where it can no longer do that. Take the gas cap off & see if the stall condition goes away.