Well it's just another case of you can believe me or not....it really doesn't matter.

On this bike if you are low on fluid in the clutch system it can cause slipping.

It may be counter intuitive but it does happen.

So like I recommended, pull the slave cylinder and disassemble it. Check for scoring in the bore. If it is FUBARed then you are looking at around a little over $100 for a new assembly.

If it is good or at least decent you can replace pos #9 Honda, ATV Parts, Scooter Parts, Motorcycle Parts,CRF,CR,MX Parts, Goldwing parts

and see if that fixes the issue.

Or you might get lucky and a good cleaning will rectify the issue.

Its not just low, it is entirely empty. I also believe it is leaking and that's why the slipping has gotten progressively worse. I will take a look at it this weekend.

While you're at it, check the fitting at the the end of your clutch line to insure that it is tight and has the washers installed on both sides of the fitting. If your clutch fluid is low you will now have to bleed the system when you refill. There are a number of ways to get all the air bubbles out or past the upper banjo fitting.

Look below your slave cylinder and if it is clutch fluid leaking it'll stip your paint where it's leaking from so you'll know it's clutch fluid.

Generally if you fill the resivoir you can just flick the lever back and forth and it'll work the air out. The only exception is the banjo is higher than the orfice in the master cylinder so you'll likely need to bleed it at the banjo bolt as well. If you want to keep from spilling fluid while bleeding the banjo you can also take the master cylinder off the bar and tilt it so the banjo bolt isn't the highest spot in the system and pump/flick the lever and let it snap back to finish bleeding it.

Bumping this thread to ask a question...

I changed the oil to Mobil1 VTWIN motorcycle oil and saw no change in slippage

I opened the bleed nut on the slave and pulled the clutch lever -- fluid shot out, but the slave reservoir level did not change and was totally unaffected. Is that normal?

The master did lose some fluid

The clutch slave cylinder does not have a reservoir, so not sure what you are saying.

You mean to tell me that the reservoir on the clutch side of the handlebars that has lines that go to the slave cylinder is unrelated to the slave cylinder?

you have to bleed it like youre doing brakes,take your time,it is a slow procedure,but once any air in there is out.it will start to flow.

No, what he meant is that your terminology is screwed up...

The part on the handelbar is the MASTER cylinder, and it has a reservoar... The part on the side of the engine is the SLAVE cylinder, and it does not have a reservoar... When you operate the MASTER, it affects the SLAVE...

Now, common sense says that since you have bought the bike used form people that might not know a whole lot, you should change the fluids... So trying to diagnose this with an unknown fluid in there is pointless... Go get a bottle of clutch/brake fluid (DOT 4 or 5.1, don't mix it with DOT 5, they are not the same) and clean out the old, and bleed with new...

Then come back and we will figure this out...

+1 on checking the clutch slave and replacing seals, check the bore as grit can get in and score the surface making the seal ineffective. (sometimes a bit of fine wet'n'dry and polish can restore it, but you can replace the clutch slave with one from a Blackbird or Pan Euro)

When bleeding make sure you fill the reservoir little and often, as it has a smaller capacity than the front brake reservoir. A handy trick if you have a friend is to use a large syringe to suck fluid through the system while your mate keeps it topped up.

Okay, so I think my master is shot then, because it doesn't receive or return fluid at all. When I got the bike, the master was totally empty.... and when I filled it up, there were particles floating in there.

If I work the clutch with the slave bleeder open, it sprays fluid, but the master level is unaffected..

Have a hunt around for a master rebuild kit which includes new seals etc. A bit fiddly to do but the procedure is the manual.

superduty has one for sale,jump on it.

1: If fluid is moving at the slave cylinder... it can only come from the master cylinder ....

2: The master cylinder when ran dry, takes a bit of work to get it moving fluid again.... the air trapped in the cylinder can keep it from drawing in fresh fluid from the res.

3: Contaminated fluid, moisture laden fluid will grow black and or brown grey gelatinous like crud.. It can block passages in the master cylinder or slave cylinder.

4: If you want to repair your clutch system, you need to do a compleat job.... hap-hazard approach to repair will not get you a result your looking for.

5: Order the master cylinder repair parts and slave cylinder seal... You'll need some snap ring pliers and basic tools...to disassemble both.... clean with a lint free cloth and clean brake fluid... if no pitting, you can re use all parts except the rubber stuff... Replace those and reassembly.

Fill the master cyl res, loosen the line at the slave, and allow fluid to fill line to the slave.

keep fluid topped off in the master cyl res,,, work the lever and watch for air bubbles to come out of the port down in the res..... when you get no more air... start bleeding the slave at the bleed nipple.

the line itself could be clogged and stopped up,might want to see about getting a braided line or atleast a good used oem replacement.

But again, the OP states there is fluid moving at the slave cylinder... the only way that is possible is if the master cylinder is pushing it.. and, well that means the line is not blocked.

What is the condition of the rubber diaphragm in the master reservoir? Does it fit nice and snug, or does it seem to be swollen and not fit properly?

Noticed your looking at used parts.... Suggestion.... skip buying used, unkown condition parts, and fix what you have.

MASTER CYLINDER PISTON SET
PISTON SET - Search : 22886-MB0-305

And Slave cylinder parts
CUP, SLAVE CYLINDER
CUP, SLAVE CYLINDER - Search : 22865-MJ8-003
SPRING
SPRING - Search : 22864-MT7-006
GSKT, SLAVE CYLINDER
GSKT, SLAVE CYLINDER - Search : 22862-MW7-650

Guys, everything that he just described leads to a plugged MASTER cylinder. The return port is plugged and not allowing fluid to return to the res. When the bike heats up the fluid expands which in turn starts to DISengage the clutch. When he cracked the bleeder on the slave and fluid "shot" out tells me that the pressure was locked in on the system and the clutch was still partially disengaged.

Hanger, completely disassemble the master cylinder and clean it out. There is a piston in there and there are some tiny ports and holes and such. Clean all that shit out. Then do a really good bleed on the system. It will take you some time to get the clutch bled because there is only clutch spring pressure acting on the fluid system, so you can't build up that much pressure as you would on brakes. Keep at it and eventually you will get all the air out. One thing that I've found that helps is "flicking" the clutch lever. This will actually get air bubbles coming up into the reservoir. Once no more bubbles come up then it's time to force them DOWN. Rapid squeeze-hold-loosen-tighten-release cycles will eventually force the air down to the slave. Keep an eye on that res level, as it can go down pretty quickly and if you suck air again then you start all over again.

Good luck.

PS You should only need new parts if upon disassembly you find that the rubber components on the cylinder are torn, worn, or breaking down.

It is fixed.... turned out to be a nasty air bubble. Though I probably will follow the above advice because the clutch lever feels slightly spongy