I'm a cheap guy and I like making things myself. So when I was contemplating replacing the stock air filter on my 1974 CB350F, I decided to give the following a try:
The stock filter on my machine wasn't too clogged looking, but it was probably the original from day one and the cloth element was looking quite "fizzy" and not very clean. The filter itself is in a nice solid-construction case, so I went ahead and cut and ripped the old element out of it. Then I went to my auto parts store and found a round auto filter that had the same depth of element. The auto version seemed about the same material as the original for the bike, except of course in much better condition. The price was cheap too! Some cutting of a section and removal of the wire mesh covering on the auto filter, and I had some new element to slip into my Honda shell. I also trimmed some of the vinyl rim off to make it fit better. Then I sealed the edges up with some auto goop (a common sealer/adhesive that most auto places stock in a tube...most handy stuff...looks a lot like clear silicone caulking seal except cures harder and really sticks). The pleats of the filter element on the re-built filter aren't as neat looking as the original, but I expect it will do the same job, and besides - it can't be seen anyways.
If I had been more careful in my original measurements and had cut a longer strip of filter element, I would have had enough left over for a second filter. At least the auto filter was big enough to get a second chance. Anyways, the cost was still a lot less than what I've priced for new replacements.
