Clutch Or Brake Plugged Return Port
Clutch works fine at first, but after riding for some time, begins to slip.
Brake works fine at first, but after riding for some time, the brakes won't release after being applied or will apply all by themselves.
Pump clutch lever repeatedly to see if slippage can be induced. If so, the return port in the clutch master cylinder is probably plugged.
Ride and brake repeatedly to see if the brakes won't release. If they won't, then the return port in the clutch master cylinder is probably plugged (alternative culprit is stuck caliper pin).
The easiest way to know for sure is to open the lid on the reservoir, remove the splash guard over the return port, squeeze the clutch lever and then GENTLY release the clutch lever. If you see a squirt forming in the reservoir as you start to release the clutch, your return port is fine and you should look elsewhere. If you don't see any action in the reservoir, try releasing the clutch lever with normal action. If fluid does not fly skyward (protect your paint first), the return port is plugged.
Quick and Dirty Fix
Crack the bleeder valve on the offending slave cylinder/caliper(s) to relieve the pressure to get you home.
Unplug the port. Can't find it? Cliff Koch writes:
[On the master cylinder] there's two holes. A big one that sits between the outer piston seal and the main piston seal, and a much, much, smaller hole just in front of the main piston seal. The big hole is to fill the area behind the main piston seal with brake fluid so that the bore behind the main piston seal remains submerged and lubricated with non-pressurized brake fluid. The smaller hole is to allow fluid to enter/leave the hydraulic system when the lever is at rest for things like thermal expansion or filling the slave cylinder as thing wear.
The smaller hole usually has a little plate that covers it that's held in place by some castings around the larger hole. The plate is there because when you first start applying the lever and before the piston passes the little hole, fluid is pushed out of the little hole with a fair amount of velocity. If that little plate isn't in place when the lever is pulled, the fluid can hit the ceiling. Again, don't ask how I know this.
If you have a problem finding something small enough to clean out the return port, get yourself over to Wally World and head for the sewing section. After going through my small stuff, down to the #80 drill at 0.0135 inch I found that the smallest needle in the Singer brand assortment of 45 "hand needles" worked fine. Cost all of $1.25 so it is a Maggot priced tool too. UPC 75691 30020 Jim Mc Adams