Motorcycle Repair: cb900c running problems, motorcycle repair shops, valve shims

Question
hi bill,I'm waiting for the rotor and rectifier to come in.had to buy a compression tester.will check compression tomorrow.not clear on what compression should read or what size valve shims to use on the 1981 model or a good place to get them from.I also noticed the exhaust from the right side tail pipe is a great deal "weaker" than out the left side. thanks, trent

Answer
Trent, to test compression hold the throttle wide open (KILL SWITCH in OFF position) and crank engine for about 10 seconds or until the gauge reading stabilizes. You are looking for readings around 170 psi. If your readings are more than about 5% off from each other, then check valve clearances. If clearances are within range (.005") and compression readings are still out of range, then either valves are worn/damaged or the rings are worn/damaged.

Check local motorcycle repair shops for shims. Often they will exchange them for you or I think that K&L supply dealers offer them for sale in various thicknesses. You have to use the removal tool to R&R them.

Measure your clearances first, making a chart of what you have now, then you will have to remove each one, measure the thickness and determine how much of a change you need to make, one way or the other. http://www.youtube.com/watch?v=elKilUuKM8U

With the valve cover off, you can visually check for camchain slack and make your adjusments as necessary.

"Weak" exhaust pressure can be due to low compression or cylinders not firing properly due to spark/fuel problems.

Bill Silver