I have my 02xr4 snorkel out and wondering which is the best prefilter to use over the airbox hole? I seen the helix pre-filter comes in 1/2inch and 3/4 inch and maybe 1 inch thickness. Wouldn't the 3/4-1inch thickness stay in place better between the airbox and the frame? Is there any other prefilter material that filters sand better than the helix pre filter material? Thanks for any help!

Pantyhose.

I have used Helix 3/4 filter coarse foam.  There are photos in the FAQ.

thanks guys, i will go with the 3/4 helix foam and i will also try the panty hose as it seems real fine and seems like it would stop very small grains of sand!

My bad pantyhose experience-----the first time i went to hooters restaurant and seen all the hot legs and booty walking around i loved it, then i seen up close they all have to wear a light whitish colored pantyhose which covered up all the sexy skin, what a bummer!!!!

Edited by XL100allnightlong, 23 June 2012 - 09:04 PM.

You could also grab some of the sanitary foot covers they have in shoe stores when you dont have socks to try on stuff. They would be the perfect size. Im using a a/c window unit mesh filter matterial, its about 1/16" of an inch thick, I just cut it slightly larger than the airbox hole, then used one of my girlfriends hairties to slip around the lip of the airbox rim to hold it on. It looks and works great. And the filter material was like $2?

Isn't stopping dirt what the air filter is for?  If not then why weren't you running a prefilter with the snorkel in?  I have the whole top of my airbox cut off and have never had a problem. Just keep your filter cleaned and oiled.

I'm with Shrk352 on this one. Why pull the snorkel for the extra air flow then restrict that air flow with something else? I've also never had a problem with extra debris in my air air box in the 9 years I've run without the snorkel.

Even with a un-restrictive prefilter over the air box hole, the engine completely rips compared to having the snorkel in. I test my bike on a quarter mile "maybe a tad longer" strip and noticed no difference in mph with using the uni filter/ or the stock filter. Also with a prefilter on it made no difference in mph. IMO with the snorkel in, at mid-high rpms the engine cant suck enough air through the small intake of the snorkel which slows the top end down. But with the snorkel out I see no difference when using a uni/stock filter or prefilter with mph, it hits a steady 82-83mph everytime. With the snorkel in the bike, it would only hit 77-78mph.

My bike keeps getting sand in the airbox and I find it really annoying. I still have to try the pantyhose trick over the airbox and see if that keeps the sand out. These uni-filters seem to let very small particles of sand through it and it is not acceptable to me. Maybe the stock filter will do a better job? This is why I want a good prefilter!

Edited by XL100allnightlong, 28 June 2012 - 07:53 PM.

When I got my xr400 to Oregon, my friends helped me set up for the dusty trails.  They added hand guards and a pre filter.  it keeps the air box clean,the air filter cleaner, and I can't tell any difference withit in or out.  If I ride a dusty trail and think the pre filter is clogged, I can open the airbox, reach up, and pull it out.  Then ride with an air filter that is pretty clean.

Here is The thread on pre filters.
http://www.thumperta...250-pre-filter/