Ill try to make a long story short. Quad has sat for extended periods of time. Last time it sat we took it in and had the valves adjusted tune up etc. Not long after that it sat again for a while, like maybe for 1 year. Now when i can get it to start it pops and sputters. I replaced the plug and added fresh gas to the tank (It was almost empty) Still does it.
Does this sound more like a bad valve adjustment or am i need of a carb rebuild/cleaning?

If it is a carb issue is there any good write ups on how to rebuild a 400ex carb?

 

The most likely culprit is a gummed up carb/jets from sitting with gas in the float. I am sure you could do a youtube search and find a decent tutorial. If it doesn't have many hours since the last valve adjustment I doubt it would be the issue. BTW, adjusting the valves on that should be pretty easy as well, just need a feeler gauge and a little patience/common sense.

 

Air filter clean?

 

sounds like you are running a little lean. Might be a fuel or carb issue