Motorcycle Repair: clutch, clutch friction, clutch adjustment

Question
I bought a 1978 cb125 recently.  After it sits overnight, when I hold in the clutch and put the transmission into low, the bike jumps ahead and it seems like the clutch is still engaged.
After the first time and when the bike is warm this doesn't happen. What could be going on?

Answer
Jim, I will assume that this little bike has been sitting for a long time, somewhere. What often happens is that the clutch pack sticks together and the best way to fix it is to disassemble it and replace or clean the plates. The steel plates get rough with either rust or clutch material that bonds to the metal and that can cause rough engagement and disengagement.

Now, it is pretty normal for bikes to tend to clunk into gear or jerk forward slightly, when they have been sitting overnight or for a few days. If we assume that the clutch is generally okay, perhaps you can look at the clutch adjustment. If you have excessive free-play at the lever, then there is less disengagement travel available to release the clutch plates. If that is the case, then tighten up the clutch cable play, until you just have an 1/8' or so at the lever before you feel it start pulling against the clutch assembly. If the play is adjusted correctly and it is still grabbing noticeably, then you can try changing to a different type or grade of oil or buy a clutch cover gasket and any seals for that side and take it apart for a clutch inspection and repair.

If you have doubts about the condition of the oil, then change it and use a good quality motorcycles oil. If you change it yourself, take a look at what comes out to see if there are any larger sized particles that would indicate clutch friction material and/or rust from the stuck clutch scenario.

I would change the oil, adjust the clutch, ride it around for a few hundred miles or a couple of days and see if that changes anything. Again, there is a natural tendency for a "first thing in the morning clunk" in most any motorcycle, so depending on the severity and duration, it may just be normal.

Go to BIKEBANDIT.com for online OEM microfiche illustrations of the parts involved.

Bill Silver