Sounds like you have some adjustments to make man...
First, wiht the slef off, check to see that you have about a 16th of an inch between the throttle and the bars when the throttle starts to pull on the cable... if not adjust the cable (if one carb adjust on top of the carb, if more than one adjust where they meat so you dont throw the carbs out of sync.)
If all is good there and the sled still does not idle right then start up the sled and havea buddy help keep it going if nessassary and adjust the idle screw (side of the carb(s)) VERY SLOWLY and have youre buddy let go of the throttle and see if the sled will idle by its self, if not, keep adjusting the screws... I dont usually like to do this my self because I would probably not adjust them evenly and that would cause one cylender to run faster/slower than the other...
I am no expert but I did my best, hope this helps!