YH50 starting problem

[never too old to ride]

After topping up with fresh fuel my wife's YH50 wouldn't start, topped my bike up at same time no problems. Cleaned plug topped up charge on battery and managed to get it started it revved well with the rear wheel off the ground but when the throttle is released it died and will not start again, any ideas

[Airhead]

maybe a blocked idle jet?

better still maybe a blob of water in the carb...is there a drain plug/screw on the carb bowl?

[Variomatic]

Like airhead said, maybe a mucky carb. Has it sat for a while?