I changed the gaskit / diaphram on mine , much better now.
This fits between the carb and the tank and seems to be part of the mixture control system.
£2.35 from Ebay ,
http://stores.ebay.co.uk/Terrys-Chainsaw-Chain
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&rd=1&item=260231055453&ssPageName=STRK:MERFB:IID
Ian Paul
May 2008