Just so you know in the future, you can take the carb apart a few times without worrying about replacing the gaskets. Glad to hear you got it cleared up!

 

a friend of mine has a 2000 big bear 400. it was doing exactly the same thing. took a while but we finally found out what happened. where the front of the carb goes into the intake tube on the back of the head, the clamp had come loose. this allowed the carb to move and at half throttle or better or over bumps, the carb would come out of the tube enough to allow air to get in causing it to sputter, pop and all kinds of things and then stop running. try loosening the clamp real good, push the carb back into the tube and retightening the clamp, theres not much of a lip on the carb to push into the tube, not even a quarter inch so make sure you hold it tight while you are tightening the clamp up otherwise it will pull right back out.

 

I got 2 2000 400 big bears that are doing this. One I just bought for almost nothing, havent got a chance to look into it yet. The other I have owned for 3 years. She idles perfect, but when you give her half throttle she spits sputters backfires and floods. Right after it started this I tood the carb apart, it was full of trash. Cleaned it up and it ran great, for a couple month. then it started again, I took the carb apart again but its still clean. Had new gas in it. Lines are new, filter is new, everything is hooked up tight, what else could it be? Bad needle seat? the bowl was totally full of gas when I took it apart.

 

definitly get a inline fuel filter all quads should come with one from factory in my opinion their inexpensive and save a lot of headache glad you got it fixed