I have a 1997 Kodiak 4x4 400 that I bought used from a dealer with 235 miles on it.. It look like new but I could not really ride it at the dealer. I got it home and rode 15 miles and it started leaking fuel out of the overflow.. I also noticed at wide open throttle it will start cutting out and backfiring until I take it to about half throttle. I assume the float is sticking or dirty.. This quad sat a lot and was not used much. However, I also noticed the quad leaks fuel out of the petcock even when it is in the off position!! This just does not make sense. I will buy a new assembly but does anyone know what to do about the back firing and running rough at open throttle??? Also, is there anything else I should do other than replace the needle and seat???? Please let me know??

 

Yep, sounds like the needle and seat are staying open.
Before buying any parts, try cleaning them up, with scotch brite, or steel wool. Usually thats all thats needed. Polish both the needle and seat.
The backfiring is probably a lean symptom.
Try this, run it with out the air box lid, for a test drive. Do the symptoms get better or worse. If it gets better, then the carb is too rich, and a high fuel level, could be the cause. If stopping the leak, doesnt get rid of the backfiring and stumbling, then the jets may need changing.
Then try running with the choke on, or with the air snorkle, covered with duct tape, about 50% closed off. This will make it real rich, and if it runs better that way, then the jetting is lean.
Your main jet may be plugged, so when you take it apart, clean all the jets and pasage ways.
If theres alot of crud in the float bowl, then you can assume the passages are plugged.
heres a good site on jetting and symptoms of lean and rich running.
jetting