How to balance a Model A carburetor

Can anyone tell me how to balance the Model A carb? I'd like to use an air filter with the stock carb but I know it has to be modified (balanced). The stock carb fuel bowl is vented to atmosphere. When the air filter restriction is added it causes the engine to run rich unless the float bowl is at the same pressure as the air inlet. I've seen instructions on how to do this somewhere but don't remember where. Can someone help? MANY THANKS!!!!!!<!-- / message -->

 

Really? I've never heard of that in my 6 years of long distance driving with the Dallas Model A club and all of their cars, too.

Only issue I've had was when running an air filter on a stock Model A carb, the air filter got so hot being close to the exhaust pipe that I had to take it off. The car was vapor locking like crazy, slowing down to only 20 mph was as fast as it would go.

I first thought my points kept closing up and kept making sure my timing was right. I finally figured out it was the air filter.

When I went to take it off on the side of the road, my wrench was making sizzling noises as I loosened the bolt on the filter. Threw it in the trunk, let it cool down, and then drove for 3 hours with the pedal to the floor at 50 - 55 mph without that stupid air filter on there back into Dallas.

 

Here is useful info on the air filters:

http://www.model-a.org/filtering_air_into_carb.html

 

Zenith balanced some carbs that were developments of A-B carbs with a cast-on tube, but those were for combines that ran in a cloud of chaff.
Think about this...vast numbers of cars made up til modern emissions about 1969 ended atmospheric venting had bowls vented only to atmosphere and of course hd aircleanes of all types, paper--wire mesh--oil bath. This is only a problem if air cleaner is restrictive, either from bad design/small size or dirt ac***ulation. Zeniths used on Model B Fords had crude aircleaners from the factory and were not balanced.
That is, Ford and Zenith did not see a need here.
Use an air cleaner that is big enough, preferably with a modern paper filter, and change it when dirty. If you have run the car stock with no cleaner, you know what GAV setting it needs when warmed up. If you need to crank GAV in leaner, your aircleaner is not big enough or needs cleaning/change. I think the supposed balancing arises from using the old Air Maze with its small, primitive element or the same castings with tiny paper filters from small industrial engine filters. Some of the little hotrod chrome dome filters aren't much better.
Use a fairly big filter, with some tubing to connect it since htere's very little room near airhorn.
The way to balance typically is to tap the vent area in the area beside the bolt under where the two castings join and run a tube back from there to another fitting tapped into rear of airhorn.

 

PS...Vizard flow tested a bunch of large filters on a 750 carb, and registered no flow loss with the better paper filters or with KN. In the real world, you need a filter with excess capacity do it works with a good deal of dirt aboard.