I recently purchased a 2000 400ex and have been riding frequently for about a month. Recently, I noticed that the chain had far too much slack in it and was hitting the swing arm plate. After adjusting the chain, according to the manual, it seems as if it just gets loose again immediately. I also noticed that when pushing the atv backwards with the handlebars turned, the chain becomes very tight. I am new to this, but the rear axle seems to have far too much play in it when the tires are off the ground. All bolts are tight and I am wondering if I am doing something wrong. Any advice would be GREATLY appreciated. Thanks

 

You are probably due new axle bearings. They don't seem to last very long. If they are worn, get them changed. If ran too long they will ruin the carrier, that is expensive.

 

Yep, your needing rear bearings. its not that bad of a job should be done with it in no time +)