spudulike

Hi Spud. You seem like the go to man for help sooo Here goes. my 346XP has developed this problem. Work it in average wood for a few mins and it gradually does this - throttle off and the revs wont drop instantly it runs on slowing gradually and ends up with a fast idle , open the throttle and it is reluctant to pick up but eventually does . progressively becomes worse . turn it off cos its impossible to work with . I took it to my dealer who said carb problems and fitted a brand new carb - - £ 140 later exactly the same ! I opened the fuel cap to vent it and it went for a few mins then started playing up once more . Could it be something as simple as the tank breather not working ? ? Regards Andy.