need a easy way of testing to see if drive belt needs replacing from stretching.

 

If it could stretched it sure would slip. When a belt does finally need changing its not due to stretching but more because of width wear.
Here is a good read Dirt Wheels Magazine | CVT BELTS: Secrets to keep your belt alive.

 

Easy on non ebs systems. Just place a straight edge on top of both clutches and pull down on the center of the belt. If top of belt is over 1 1/2" from the straight edge,probably time to replace it. Plus always check for any burnt/glazed edges on belts also.Has shims you can remove inside the rear clutch to take up some slack,but usually not enough. Just replace one it gets this much slack. Always use the oem belts. A lot of people have had problems on after market belts such as creeping because of belts being too wide.

 

If you need help on changing a belt here is the easy way. the guy only took his clutch of to inspect it.

 

The performance of your quad will suffer with a worn belt. It will feel like the engine is losing power. Belts wear out generally. They're rubber, the friction eventually will burn off a small amount of material making them slip. You might not even be able to look at it and see the wear. Just a very small amount of wear that might be hard to detect visually will result in loss of power. If its got a lot of miles on it, there's a pretty good chance it needs replacing. Oem is always the best. Perfect fitment and generally better quality than most aftermarket belts. Oem will last longer.