My neighbor gave me a .40 rossi engine a few weeks back and I cleaned it up and noticed there wasnt a place for a pressure line from the mufflerto the tank. Do you need the pressure line, and if not, how do you keep the tank from making a vacuum?
Also, on the bottom of the muffler there is a screw which i have deemed pointless. does anyone think this could be a place for the pressure line?
Any help is appreciated.

Both of my Rossi's (a .45 side exhaust and a .61 rear exhaust, I purchased new without mufflers and I think this was common for this engine. I used aftermarket Full wave pipes for both and both use pressure taps for the tank.

Can you post a photo to show what kind of muffer you may have.

When operating an engine that does not need a muffler pressured tank then the tank vent is with a short fuel line looped upward to face forward or angle cut to face forward.

John