--Problem solved; it was the carburetor: the float valve piston was stuck in the narrow tube it should slide freely within. This has now happened twice, including once at Burning Man this past week.
--Now for the new problems! In the past week the following things have happened:
-Key broke off in ignition, but a guy showed me how to get it out with a neat tool called a key extractor.
-Fuel leak for unknown reason; I suspect dust screwing up the vacuum flow control but haven't had time to investigate. The leak was seen dripping out of the end of the Uni air filter.
-Car wouldn't start, even with charged battery. Problem appears to be dust in starter motor causing brushes to lose contact; will have to detatch and examine soonest to see if that's indeed the case.
-All in all I'm finding it hard to imagine one of these Chinese things being terribly reliable for anyone, anywhere . Admittedly things were pretty harsh where I spent last week but I'm beginning to think of the whole offroad kart thing as a huge mistake. At present I'm looking for a way to replace the powerplant altogether, upgrading to an engine that has parts that are a little easier to find. Any suggestions appreciated.