Alan
I too have a sherco 50 that you made a rear brake pedal for.(excellent job by the way thank you!!)
It had some foam cut into a small round circle and placed in there from the previous owner. I never could get the bike to run right or consistently. It actually ran like it was running lean when common sense would dictate with more air restriction it should run rich!!
After a call to ryan young he said no one has been able to come up with a good fix and that my poor running problem was caused by foam air filter.
He was 100% correct I removed foam and bike runs fine!!! My guess is lean condition was caused by lack of "signal strentgh" to pull adequate fuel through main jet.
I was still not satisfied with air filtration so I went back to an old trick I use on all my other dirt bikes and that is a product called "filter skins" made by PC Racing http://www.pcracingusa.com/index.php
these have worked great and I use them on all bikes to lessen air filter changes since they catch the bigger stuff. Just put a little air filter oil on them and voila!! I even clean them a few times before disposing of them
Finally I also have a bete 50 with the same air filter as the sherco but with more room behind the carb so beta put a little airbox that attatches to the carb. It still only has the same mesh airfilter so I wasnt happy with that setup. As soon as we got the bike I used some of those little 1 inch round airfilters you were talking about and blocked off the open part of the airbox. Now bike breathes through those 1 inch filters. This didn't cause any performance problems on the beta. I did this mod in 5-04 so it was hard for me to believe foam in the aircleaner on the sherco would cause a problem but it did. Thanks Ryan for your help on the sherco!!!!
Hope this helps other people because it was a pain for a while for me!!!
Tom Bledsoe