Difficult to say without more engine details, but you are describing classic symptoms of fuel starvation.
If the carburettor has a float chamber, drain it. It is likely to contain a small amount of water that has condensed in the tank, and 'sunk' through the gas (it's heavier than gas), and ended up in the carb, where it will block the jet.
phil_saunders@bigfoot.com
Phil Saunders
May 2008
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