[pat in Santa Cruz]

I made up a filter horn using a piece of 2 inch copper street 90, shortening the flare end by 1/2 inch and soldering the cut off piece inside to bush it to fit the carburetor. Then I adapted the filter element flanges from an A airmaze to the horn and to accept the longer filter element. Since then I have seen the aluminum Airmaze horns meant for A's used by routing out the inside with a carbide bit until it fits the carburetor . That's cheaper, less time consuming and easier than modifying a copper 90. I use the 5 or 6 inch K&N filter, which number I cannot remember. I found it in their catalog.

There were filters available for B engines back in the day that were filled with oil soaked steel mesh/ heavy steel wool. In both cases of an A or B zenith, using the filter with the least restriction as possible is best, as neither carburetor has an ambient air tube to the fuel chamber from the intake side of the butterfly to equalize the air pressure. Using a more restrictive filter, such as paper or small surface area will result in a richer running engine. My experience with the low restriction elements is good as far as engine performance goes. The smaller paper elements made the engine too rich. Both the larger and smaller paper elements can get pretty clogged up if the carburetor leaks and soaks the element. In the case of the K&N or oiled steel mesh, any leakage just washes out the oil.

I only use the elements during dry weather anyway. The engine still seems to run better without any element, but that could be attributable to the moisture in the air or the cold air in winter and not the lack of a filter. Its all subjective on my part anyway. I haven't seen a definitive tests, like dyno tests to verify any of this. Opinions on filters will generate as much difference of opinion as what oil to use, Float O Motors, or whether or not to use marvel mystery oil.