Air Balance : Marvel Carb?

[duke36]

Does a Marvel Carb need (or is there a method) to be air balanced for an air filter ? Also, should a drip hole be provided in the air throat bottom ?

 

[alexiskai]

They do need to be balanced for a filter. Dave Renner can do it, I'm not sure what the procedure is. (He'll do it, but he doesn't believe in adding air filters unless you're on dirt roads.)

 

[AL in NY]

IMHO, air balancing isn't necessary if you run a high flow air cleaner.

 

[nkaminar]

The original Zenith carburetor has the float chamber open to the atmosphere. A restrictive air filter will act like a choke and suck fuel from the float chamber. An air balanced carburetor has the float chamber open to the inlet side of the carburetor upsteam of the choke. So a restrictive air cleaner will balance the pressure inside the throat of the carburetor with the pressure inside the float chamber. This means that extra fuel will not be sucked from the float chamber.

This principle applies to any carburetor. An antique carburetor that was designed to be used without a filter can be modified by running a tube from the atmospheric vent on the top of the float chamber to the inlet of the carburetor just upstream of the choke.

 

[SAXBY2]

Is this what is intended from post 4? A tube (red line) from the vent hole to a position on the throat ? Also, this Marvel has no drip hole for fuel in the intake.

 

[Bob Bidonde]

Any filter placed on the carburetor's inlet will degrade the engine's ability to breathe, so performance suffers. In short, volumetric efficiency goes down.

 

[nkaminar]

Sax, Yeah, that is the idea. Has to be before the choke. I have no experience with the Marvel carburetor but if it has the float chamber vented as pictured then it is an air balanced carburetor.

Race cars don't have air filters unless they are running on dirt roads across deserts. The engines in race cars are rebuilt on a regular basis. Any modern car that is expected to last 500,000 miles has a filter. And an air balanced fuel injection system controlled by a computer with a sensor to measure intake manifold suction pressure.