well im gonna carry on this thread on my own lol as i know there is not a lot of info on KTM 640 LC4 aftermarket air filters around, the only one i have found is one K&N made for a while where you had to rip out the whole airbox and fabricate a metal tube to connect it to the carb. But that air filter is no longer made....so im writing this in the hope it will help people in the future
Ive gone ahead and ordered it, at a great price (?25..else where its ?40+)
Ill be back when it gets delivered and ive installed it..
Filters like that typically offer much better flow then a paper filter (which is what they usually replace). You are not likely to see any real improvements using that in place of a foam filter, other then it should last longer.
Biggest thing to watch out for with those is keeping it clean. They tend to not look as dirty as a foam filter would yet they get dirty and the dirt dries them out so they do not filter as well. Yet it is not as obvious when you look at it that it needs cleaning.
Also, avoid using an oiled gauze filter in wet environments as water washes through them and carries dirt with it. I would think the same could happen with a foam filter but foam seems better suited to use in wet and muddy conditions.