Yamaha Yamalube Biodegradable Air Filter Oil. Expensive, but environmentally friendly and VERY sticky. Put a bit in a big Ziploc baggy, as the clean, dry filter, and squish it around. A gallon size Ziploc is big enough to squeeze out the excess without wasting any oil. Zip the bag shut and save the squeezings for the next filter cleaning session.
The airbox is designed to reduce intake noise and to keep the intake high and dry during water crossings. Therefore, it is somewhat restrictive.
One way to reduce restriction is to drill holes in the plastic cover that is removed to service the air filter. Expect the engine to run with a leaner mixture and to generate more intake noise. The lean mixture is easily rectified by careful carb tuning, but you'll just have to live with the noise. One problem with a drilled airbox cover is that you'll loose nearly a foot of depth capability in water crossings. Water ingestion is not good for an engine. The plastic side cover will provide adequate protection from splashing in shallow crossings and in rain, though. One can carry waterproof tape and in case of a deep crossing simply tape over the holes. After crossing remove the tape to restore the benefits of the ventilated airbox cover. Also, one can extend the altitude range of good engine tune by drilling the airbox cover, then taping the holes at lower altitudes. Once riden high enough the bike starts running rich, remove the tape to lean the mixture and restore good performance. When returning to lower altitudes and the bike starts running lean, retape the holes to richen the mixture. If a holy airbox cover bothers you a new one can be ordered for about $35.
When I get around to building a 276cc TW with a 6-speed trans I will design and build an aluminum airbox that will flow much better than stock. All I have to do is win the lottery so I can afford the build.
