Clutch test

Pretty easy to tell when you ride the bike. If it slips a lot, you'll smell it. If you got good traction and the bike doesn't react to the throttle, provided all else is well, (jetting and such), it's slipping. You also can take the discs out and look at them and measure them. But you should be able to tell from just riding it.

Ride the bike in third gear where you have excellent traction(pavement). Drag the front brake while tunring the throttle on if the revs go up without an increase of speed your clutch is starting to slip and needs replacement.

there is a very simple trick:
start the bike, put it in first or second gear, press the rear brake and release the clutch slowly. If the engine shuts off, the clutch is still good, but if the engine is still running, you need a new clutch.

Do like Halfast816 said but use your rear break instead.

If the bikes RPMs go up when you step on your rear break you need a new clutch.

Also, for longer clutch life, change your clutch springs every couple of months. It doesn't seem like a big thing but it really helps and for around 15 bucks its worth the price. They are under tension the entire time and if left in for a prolonged period of time they wont work as good as new ones.

I am not a big clutch user but I can tell the difference when new springs are installed.

You should also check your basket, inner and outer and the clutch hub. If they are all grooved up you will need to either file them down or replace them with new ones.

Good luck man

Find a nice straight an power shift through the gears. You'll tell if it's slipping. lol

Yes rear brake, don't know why I typed front..........must have meant the other front brake that stops the rear tire. Well I usually make one mistake a year glad to get that out of the way.