help with Xiandu

This is something I'm extremely curious about. Has anyone ever attempted to buy a quad (or any other vehicle) from an impound lot? I've always wondered if this could be a bargain, or a waste of time. Google searches do turn up some helpful results. Looks like the state of NJ holds auctions online which I'd be a bit hesitant about.
 
My online searches haven't really turned up any results of anyone buying an ATV this way. I'd be really curious if anyone tried this, or knows someone who has. I've actually found a couple pages with online auctions for my state, but none had ATVs.

If you had to choose one mod that you couldn't live without, or had to recommend one what would it be? 

I am working on a basket case for a friend.  It is a 98 Big Bear (YFM350FWB).  It came with a parts machine which is a 96, which I am coming to find out is VERY different from his machine.
 
Anyway, first thing is first.  I checked compression, 150psi.  Valves are set correctly, and the engine is in time.  I cleaned the carb, and there was some junk in the passages.  It is a chinese carb, which I figured from the lack of markings or lettering altogether.
 
The bike runs.  It idles ok, but breaks up badly under acceleration.  Pulling a new spark plug shows it is running lean.  White strap, with no black whatsoever.  So I have the carb adjusted with the mixture screw out way too much (about 5 turns), and the diaphragm needle lifted to the top slot.  It is still not getting enough fuel (or too much air).  It backfires through the carb, and cannot get above idle without carrying on.  The carb boot is in good shape, so it isn't pulling any air there.  I did test this as well by spraying ether around the boot when running, looking for intake leaks.
 
Anything big I am missing here?  I am starting to believe that this chinese carb is the issue.  This quad came with the original carb, which I would like to rebuild and use, but the mixture screw is totally stuck, and stripped way down in its recess.  
 
Thanks for any assistance.

I'm assuming, it's alright to test the engine after adjusting valves without the rear axle installed? Can someone please verify this? I'm waiting on axle parts and wanting to get that done while waiting. Thanks! 🙂

The choke lever doesn't stay in position on my 2001 Yamaha Kodiak.  The model is YFM 400.  I have to hold the lever to the choke position manually for some reason.  Any Ideas as to why?