You get 50hrs out of an air filter? I don't get many more than that out of a set of rings.
Just goes to show that the variables run far and wide when it comes to these things, and as such no one magic number is the 'right time' for maintenance.
On topic of air filters though, I think washing them does allow a certain amount of fine sediment to be distributed through the filter that otherwise wouldn't have been. The act of taking something dirty and submerging it will do that. Rinsing and rinsing helps, but I doubt anyone ever gets 100% of dust/dirt out.
I'd love to either keep the filters on longer, or replace with new items more frequently, but I don't have much option. A single day out for me is around 3-4 engine hours, and I'm lucky to get 2 rides before the filter is either caked up, soaking wet, or both.. to the point you can notice the difference in performance.
Most guys around here will change them out much more often.. I don't like the task, so I avoid doing it until it's really, really, really needed. LOL
I have a theory;
Each time a filter is changed, it increases the odds of stray bits of dirt getting into the intake tract. One un-noticed stray bit the size of a typical piece of sand can cause a lot of damage.
If the filter foam is in decent condition and well oiled, and properly installed & seated, it will stop all but the smallest particles. The dirt that gets trapped outside helps stop other dirt and so on.
The filter has to be pretty heavily caked before it starts to impede performance. The bike still seems to pull strongly even when there's an 1/8" of caked dirt all over the outer surface.
When I do change/clean the filter I use varsol, then vaccuum the filter with a shop vac, as there is always stray bits of junk still in the foam. (this is important IMO) I vacuum it thoroughly- first the outside, then the inside & focus on the inside until I cant see any more foreign matter.
I then thoroughly clean and vacuum the intake tract before the carb, and all around the filter mount and airbox before re-installing a fresh filter. A filter clean/change often takes me an hour, hour and a half or more, as it takes quite a while to go thru all the process and make sure everything is right before I'm happy.
I seem to get fairly long service out of my top ends compared to many others, so this approach seems to work, in my experience.
My riding style may help to a degree. I'm not afraid to get on the pipe, but only do so when absolutely necessary, or when I want a rush & tend to ride a gear high and try to maintain momentum thru stuff. I'm not the fastest guy and certainly not the slowest either. This approach seems to help make the rest of the drive train last longer as well....
Local conditions are certainly a factor. If all my riding was in a dusty desert, I'd be miserable with all the filter changes Id need to do.
