I was asked to troubleshoot a rattling noise on an '01 Bayou 220 recently, and I searched the web extensively for information, and did not find any. This noise was definately from the engine, and only heard upon deceleration from high RPM. I suspected the can chain, tensioner system, or guides, but I was wrong. I found that the springs inside of the centrifugal clutch had come loose. 1 spring got mangled fairly badly, and another was slightly deformed near one end. The replacement clutch was $166.00 + shipping from bikebandit.com, as the springs are not sold separately. The bushings for the shoe pivots were also cracked in half and some of those fell out as I pulled the case cover off.
This is the 2nd quad I have worked on that has experienced this type of clutch spring failure, the first being an Eton kids 70cc machine.
This is just an FYI, so that if anybody does hear this kind of "rattling" noise, they will know where to look.

 

Thanks for sharing. Someone probably burned the clutch to the point of tempering the springs. Could be an issue with any engine.

A friend of mine has a bayou with a rattling noise. I thought it was the cam chain as well. It wasn't. The cam lobes and rockers had been ground down. So I found a head on ebay. When it arrived, same problem.... rockers and cam lobes ground. I'm thinking there is an oiling issue with these engines. I remember talk online about the oil pump gear being plastic and breaking for some reason....