I originally posted this in the GZ250 Bike Forum.
This is not a how to for making a worn out clutch work. If your clutch is worn out or otherwise defective you should replace it. Bad clutch springs can cause similar problems. If they are bad replace them.
Read the appropriate sections in the service manual to determine what tools you need. Before you begin.
Some symptoms I experienced:
Hard acceleration as in wide open throttle. The slipping occurs in higher gears and stops as soon as you back of the throttle. This can be a bit exciting if you are trying to get out of the way of a truck at the time.
When starting up a hill in fifth gear if I didn't down shift to fourth the clutch would begin to slip. Down shifting to fourth it would continue to slip until I backed off the throttle a little and slowed down a little. After that it it was fine. This only occurred when the bike was fully loaded as in a camping trip.
Apparently, this is a common occurrence for dirt riders. They use the clutch a lot.
The clutch plates can be worn smooth or polished to the point where they do not grip each other quite as well as they should. The solution is quite simple and quite messy.
You have to take your clutch out to do this so it means an oil change. You will also need a clutch cover gasket in your hand. Trust me on this. If you take the clutch cover off without the new gasket in your hand it will tear.
Drain the oil and remove the clutch and disassemble it according to the instructions in the service manual. Once you have the clutch cage out carefully disassemble being careful not to get the plates out of order. I'm not sure the order matters much but the plates will have worn in to fit each other by now and it seems like a good idea to put them back exactly how they came out.
There are instructions in the service manual on how to check your clutch and springs. Now is the time to do that. If your clutch is OK we can proceed with getting the slipping to stop.
You will need a small piece of quality sandpaper. The wet or dry automotive sand paper will work. 200 grit was recommended but I use a piece of 80 grit sanding belt and it orked fine. What you need to do id to lightly scuff the plates with the sandpaper. If you use 200 grit or finer you don't need to be as careful. Sand the clutch pates in a radial direction. That is from the center out. Sand both the metal pressure plates and and the clutch plates on both sides keeping in the same order the came out.
Make sure you wipe everything down good and clean before reassembly. You don't want a stray piece of silicon carbide floating around in your engine. Carefully reassemble the clutch cage and reinstall. Fill with oil and your done.
Optional: You can also shim the bolts wit appropriate washers. This causes them to press tighter on the plates. I elected to do both.
After the I did this I tool the GZ out for a test ride and tried my best to get it to slip. It wouldn't do it. After two months of daily riding the clutch hasn't slipped once.
Since a picture is worth a thousand words:
Torn gasket the got fixed with some RTV because I didn't have one. It doesn't leak.
This is so I don't have to remember where the bolts go. It also helps keep from loosing them.
Look close to see the sanding scratches.
First washer didn't work. Measured the hole with callipers and took them to Lowe's with me.
This washer is just right.
Reassembled and installed clutch cage.
I was really surprised at how clean it was on the inside.