It would seem your carb needs a clean or an overhaul, this wouldn't normally be done at service intervals. Remove floatbowl & examine the float for damage/leaks(shake to hear if there's fuel inside it-shouldn't be any!)if there is fuel inside it will hold the needle valve open letting fuel through constantly and cause all the symptoms you describe-lumpy running & fuel leaking also poor MPG. Check for muck in the needle valve & the condition of the float needle point itself, should not have any grooves around it. good luck.
Chris P.Duck
July 2010
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