I reckon the answer is, you've left this over the winter and not only do you have fuel in the bowl,, you also have water. Common problem. Resolve? Remove the carb (complete with bowl). If you are not sure how to do all this, check this and other forums for A-Z removal and re-assembly. Primarily, what you need to do, is remove all residues, gunge, varnish etc. from the internals of the carb and its ancillaries, using a good carb cleaner (be careful, it melts plastic and rubber!) You'll prob find that your "primer" plunger is pretty weak and empty. This is an area of fuel supply that really DOES need to be operational, as well as that of the main jet, which is also the locating bolt of your float assembly. make sure you pay special attention to cleaning out all of the orifi on this item. Do NOT use metal wires to poke gunge out. Carb cleaner and maybe a split toothpick will do. The float itself, unless jammed, leave alone but if you do have to remove,, remember that the needle is retained only by a short spring material which seats on same area as that of the float retainer pin. To complete, get rid of all the fule in the removeable reservoir and re-plenish with fresh. (prefereably before April 2nd when PM Brown puts 2p duty on a litre of petrol!). If all else fails, a replacement carb for your version, is about £15-£20 if you shop around.. Good luck and at the END of the season, perhaps you'll remember to drain off all the fuel this time? ;-))) I can say that because,, been there, done it, got the T shirt ! :))
Andy
March 2009