My girlfriend let her 2010 Symba sit from late November 2009 until early March 2010 for her first ride of the year. It had been on a $20 fully automatic trickle charger from Walmart all winter. When she pressed the button it turned over like normal but would never start. We tried giving it partial throttle, no throttle, and full throttle(as if flooded) all with no luck. Being afraid we may burn the starter up I started using the kick starter, and after continuous kicking for 5 to 10 minutes it finally started, but would barely idle for about 5 seconds and die. This went on for an hour with the same results.
To make a long story short we now have it running good as new. First, we added "Lucas" fuel injector and carburator cleaner to the gas tank. Then I loosened the carburator drain screw. Thats the screw on the bottom right side of the carburator when sitting on the motorcycle. It is easily accessable through the opening in the right side of the engine/leg guard, and drained the fuel from the carburator through the factory installed tube that runs out the bottom. Now that the old fuel is out of the carburator bowl and fuel line, I start cranking the engine which causes the vacuum operated fuel valve at the bottom of the fuel tank to open and let fuel with the cleaner into the carburator. Then I continued cranking for a while to get as much carb cleaner as possible throughout the carburator. It would start and idle for a few seconds and die, and then I let it sit over night. The next morning after the carb cleaner had been in the carburator overnight I had it running good as new within 30 minutes of cranking, letting it idle, and gradually being able to increase the throttle.
I talked to an experienced motorcycle mechanic that owns his own small shop who said build up in the carburator from the winter sit is a common problem. And the smaller the motor and carburator, with the longer the sit, the more likely the problem. He also said he and most other mechanics would have immediately removed the carburator, taken it apart, fully cleaned it, and reinstalled it at a cost of $80, which I think is a fair price for doing all that.
I'm buying my girlfriend some "Sea Foam" carb cleaner since it also has fuel stabilizer in it, and telling her that next fall when she notices she hasn't ridden in a while to add some to the gas, crank the motor, and let it run for 5 minutes. I think this could greatly reduce the chances of this happening next year.
Hope this helps others.
Comments, corrections, and questions welcome.