Apparently you bought this one used from someone.
First, it is not clear to me what you mean by shutting it off before it was ready. What do you mean? If it is on and you shut it off, it should be o.k., anytime.
Is this a Carbed or Fuelie sled? If it is Carbed, the carbs may need cleaning. Could the choke cable be be messed up too? This would give you the rich condition. Are you idling and choking w/o eventually running it down the trail? The choke is only needed for the first 10 seconds after startup. Longer and you can fowl plugs.
Have you tried to adjust the idle? It should be set at 1500-1800 RPMs.
If it is a fuelie, is it possible a sensor is not connected or not working. This would put the thing in limp (rich) mode. But, ... I suspect you would get a code.
Did it ever run properly since you had it? Who knows what was put in for fuel before you had it. Did you add any fuel from a metal can? Is the fuel fresh?
Given the nature of your questions, I would take it back to the dealer who did the work. It seems to me that they would have had it working correctly when they returned it to you.