the alleged carb vent

I have run into several Marvel Shrebler carburetors over the years that had the "bowl vent" blocked/pluged and the symptoms are that the engine will crank and run for a limited time and them begin to have symptoms of too lean a mixture that can sometimes be helped by chocking but will eventually not even run choked but after sitting a mintute or so will start right back up and run OK for a little longer or until the pressure in the bowl becomes equal to the pressure in the intake venturi area.

I have fixed the symptoms by drilling a small hole in the top of the bowl area so that barametric pressure can enter the bowl or I have cut a small gap in the carburetor bowl gasket to do the same thing.

Or you can take the carburetor apart and vat it in a good carburetor cleaner and blow it out and then probe the vent orifices with a welders tip cleaner and put it all back together.

One of those fixes will stop the bowl pressures from preventing it from drawing in gas to the venturi area of the intake.

Zane

• Factory info

Your site was really helpfully but I keep seeing this picture show up at different sites concerning the Main jet. When did they move it to the choke chamber:^)

That was a "right on" description of that legendary vent. I don't even fiddle with them.

It amazes me as to how many subscribe to the urban legend that they have a lot to do with the way a tractor runs. Well I guess if they are totaly clogged and the carb is leaking inside and gas is accumulating down there there might be a little richness on start up.

Should be some interesting dust raised here lol.

The bowl vent itself is internal and can't be seen from the outside. They are just passages drilled in the throttle body between the float chamber and the inlet airflow below the venturi. Now the vent that gets discussed here from time to time is on the very bottom of the carb and can be seen. It's located in the bottom of the air inlet area and is more of a drain than a vent. You can clearly see it in this picture. All it is is a sintered iron plug staked in placed in the body. Its purpose is to allow fuel that may accumulate in the air inlet from a flooded condition or whatever drain out of the air inlet without admitting unfiltered outside air. They are typically plugged with varnish or painted over anyway. A functioning drain is not crucial to proper carb operation.