Go here http://www.walbro.com/parts-service.aspx Click on Walbro Parts Lookup,then Browse by Walbro Number,then pick the letters that are on your carb before the numbers and click on it. Find your carb in the list and click on it.It will give you the venturi size in mm's which can be converted to fractions by using an online converter. http://mdmetric.com/tech/cvtchtfdm.htm