its very rtich mixture,,
a rich mixture can give jerkes and the bike may stop,, and when it stops it usually take few kicks and some time to start,,
so i think if petrol is coming and ur lubrication system to the head is ok,, then u have problem with carburetor,,
ask them to solve it,,either replace carb from them or its jets,,
remember not to buy jets urself ,, not to buy carb urself,, the after market carbs are just a piece of sheeeeeeeeeeet,,
i m sure a good mechanic can solve it,, ask him to try another car on it,, or try another carb on it,,