Mine was doing the same thing ( only runs with hand over carb) turned out to be a bad reed valve.

 

I realize this is a really old post but i ran accross the same problem. after careful inspection of my carb i had found one of the manufacture's plugs had come out and that left a open line straight to the float bowl. a little silicone fixed the problem and runs perfect now. something to check for when all else fails.

 

I have a Viper 90r and I heard that the electric choke always caused problems. Many owners that had their kids racing on themm would convert them form a electric to manual choke.