Re: accidently ran without air filter. WOW! big difference, velocity stack ?? Jet siz
A good filter will be invisible to the engine, meaning the engine will run the same with or without the filter installed. If performance drops with the filter installed it's too small, too restrictive, or both.
There ARE filters out there that can both filter the air really well and let in as much as the engine can pull in at the same time, but you won't find them in China.
Cafe racers have been using nylons stretched over their velocity stacks secured with rubber bands for decades without any problems, but as time goes by even things like this can be improved upon and several years back a company called Outerwears started making rain socks for motorcycle air filters to keep them from ingesting too much water when caught out in the rain while using a large ram air filter sticking off the side of the engine. these things are coated with a hydrophobic coating so the water can't stay on the sock and sheds off before it can go thru it, but what's even better is that they add no restriction to the induction system. Some of us realized this as well as perfectly clean filters when checked, so what did we do?... That's right.... we took out the filter and ran the bike with just the rain socks we purchased, we bought the material and stretched it over large velocity stacks and get the best of both worlds, spotless clean engines and carbs and no restriction. The Outerweras material does a great job keeping the nasties out since it filters down to .005" (yup, better than nylons, and most these restrictive stock foam or felt filter elements) but it still lets in all the air. I started using this on my Buell, then on my Harley about 5 years ago after seeing most the forum members in the Buell forum were using these, I read up on the stuff, then decided to give it a shot and I'm glad I did, 5 years later the inside of the carb and intakes still look new but there's almost zero intake restriction at the same time.
Just in case anyone is interested, here's their link explaining how these work, and they don't just make filter socks, they make all kinds of covers to protect your favorite toy from the elements like dust and mud etc...
http://www.outerwears.com/page.asp?region=17