Take a Breather

[Leviathon]

Probably a dumb question, but with new carbs on, now I have several hoses coming from valve cover breathers wondering where they go. Looks like 1 goes to flame arrestor, not sure from there. Can I just put on one of those breathers that does not require a hose?

[Fastjeff]

Here's the deal: To ventilate the inside of the motor (to prevent destructive moisture build up), a PCV (positive crankcase ventilation) system is used. A one way valve in the valve cover is connected to a vacuum source on the carb (that happens only during high vacuum conditions). Air entering the crankcase, from the flame arrestor, via a hose (usually via the fill cap or a connection in the valve cover) goes INTO the engine. The PVC valve is connected to a vacuum source at the carb to suck the air OUT, thereby creating a flow circuit to keep moisture down. Being a marine engine in a moist environment, you can see how important that circuit is!

Hope this helps clarify it for you.

Jeff

[jmonday]

I have a K&N marine style breather on mine and had to make another port for the one of the valve cover PCV like Jeff is talking about. It was on the boat when I got it and would have rather had the steel plate style. Also I think but not a 100% sure some of the mechanical fuel pumps have a hose that when the pump fails it uses a hose to the card so you do not have raw fuel in the hull of the boat.

[EWRice]

My engines have edelbrock marine carbs on them. They do not come with a vacuum port for the pcv. However, in the back of the throttle body, there is a spot for the port to be installed. I just finnish drilling the hole, run a 1/8 npt tap in and install a 1/8 mnpt to 3/8 m hose barb fitting and away we go. This is done with the carb off the engine and I blow out the port with air when done.