OK - I have a Tecumseh Carburetor 640169. It is on my Husqvarna snow thrower 927SBEXP. I have been messing with a surging problem for two years now. Mild in 2010 and so bad in 2011 that I can't stand it anymore. I have spent countless hours on the internet trying to solve the problem. In 2010 a can of carb cleaner solved it. Stored the machine empty of fuel as directed. All of my fuel has sea foam added. In 2010-11 season this this started bad and has surged bad. Starts great but NEVER stops surging. I rebuilt the carb and cleaned as best I could. The blower worked great for 3 uses. THEN - back where we started. After another rebuild of the carb and cleaning nothing worked. YES I cleaned ALL of the minute holes in the bowl nut MANY times. That is all I found on the web as to problems. After this last rebuild it was NO BETTER. I do NOT accept defeat so I got back on the web. While sitting here reading the same posts I remembered I didn't clean the IDLE RESTRICTOR SCREW (Tecumseh 640027

Idle Restrictor Screw). So I went and took the carb off for the 4,382nd time, removed the little $%$$%^$^ and cleaned the port from side to side AND directly from the end to the side to side port. (This port on the end was difficult to get "connected" to the side to side port but after some influence with a TINY wire it worked. Replaced carb and it runs LIKE A CHAMP!!!! Sorry for the long thread but I have not seen anyone post this as a solution. I hope this helps someone else in my frustrated situation. This screw can be removed without removing the carb and will be the first thing I clean next time before a complete rebuild. Part # 20 found at this link

http://www.partstree.com/parts/?lc=tecumseh&mn=TEC-640026&dn=CASERIES_AE81640026-CA