04 LTZ400 running problems

So, after having my ltz400 for a few months it ran perfect, until my carb float door broke. After replacing the carb(with a Chinese carb) and swapping the jets over from the original carb(i have an hmf slip on exhaust), I cannot get it to run properly. When I try to start it, sometimes it will start, sometimes it wont. When it does start, it only stays idling for about 15 seconds before it cuts off, it sounds like its idling perfect. Someone told me to check the oil for gas and upon checking it I could smell gas in my oil so I did a change to no avail. I'm not very mechanically inclined when it comes to carbs so I was hoping someone could help me out.

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