Two airbox mods:
After having used it a couple of years, I went to clean it again and it had holes in it!!!
I believe this was due to the extra large spring it came with that is inserted inside the filter, presumably to keep its shape and to keep it from collapsing. However I think the spring is too big and smashes the filter against the airbox wall inside, so when I bought a new filter I fashioned a square box shaped support out of galvanized hardware cloth (wire screen):
Upon more closer inspection it is now clear to me that my old UNI filter foam had degraded more than just due to pressure from a spring, and now I believe it is probably more likely due to my use of the spray Notoil oil that I lubricated it with. It could also be due to my use of a little bit of Oxyclean detergent (and hot water) when I cleaned it. I will check the 2nd Uni filter and see how it looks, as I used Notoil on it as well.
The use of issues of using Notoil on foam filters like this Uni, is discussed in the Adv XChallenge thread post 10836 through 10843.
Another foam filter now available is the TwinAir 158.328 air filter. (I was able to get it cheaper from Outlaw Racing in the Netherlands with another shipment already had coming over the pond).
I also installed a sheet of 5/8" thick Uni Filter foam for a pre-filter. It works great and catches most of the crud and much easier to clean:
And ordered this pre-filter bracket to hold it in place, from tbarstow. Except unlike this picture from Tim I still use the top airbox cover as well and put the bolts through both:
I decided to saw off the corner about 1/2", using hacksaw:
Then I took a small plate of aluminum and attached it with one screw and a lot of Permatex Ultra Black gasket maker. Sealed and as strong as hell:
I also removed the cable loom wrapping and adjusted the wires, added a piece of inner tube for cushioning and re-wrapped it in electrical tape.
It is hard to see it in the picture but there is a lot more clearance now: Before (left) and After (right):