I realize you sent me a personal email for information on the UNI filter, but I'll post the information on the forum in case others are interested. On the Batavus moped I'm using a UP-4200 Pod Filter. It has a 2" ID X 4" height. The Encarwi carburetor is about 2 1/8" on the outside and this filter will stretch over the outside of the carburetor opening for a nice tight fit. It's a little long, but it will squeeze between the frame and the carb. You can see a picture of what this filter looks like installed at my web site: http://www.geocites.com/miniengine . Just look under 'Moped Adventures' and in the HOW TO section look under the Encarwi carburetor page.
When buying these filters don't forget to buy the oil used to soak the filter. I realize UNI is trying to sell it's filter, but on the UNI web site they have information on why these filters are better then the stock setup. The UNI web site is: http://www.unifilter.com and the catalog page with the price listing of the filter I used is: http://www.unifilter.com/clamp-on.htm
scan down to the second section of this page named Uni "POD" FILTER "URETHANE END"
and you will find the UP-4200. The list the price as $13.95, but I got mine at the local motorcycle shop for $11.95. I'd seriously check your local motorcycle shops and see whether they carry UNI filters and if they will order you in this filter if they don't have it in stock.
I hope this helps,
Lamborn's Miniature Engines