Is your starter clutch slipping? Check these things before assuming that it needs rebuilt, and tearing into the engine. This list includes a issue that I recently encountered, but had never considered as a possible culprit before. 1. Make sure that you are using oil with a JASO MA rating or better.Such oils are engineered to work with wet clutches in older motorcycles, and do not contain the friction modifiers that will cause the starter clutch rollers to slip. Choosing the correct Oil for a wet-clutch Motorcycle If you do have a friction-modified oil in the sump, drain it. Replace it with a cheap oil of the correct specification, and dose the oil with Seafoam (or similar) to clear out the remains of the too-slippery oil. You can also pull the starter motor and spray carb cleaner towards the front of the engine case to help clean the starter clutch of the too-slippery oil. Do an oil change again after the slipping stops. 2. Make sure that your battery and starter motor are in top-condition. The battery should not drop below 10 volts when trying to start the bike, and the starter motor brushes should be inspected and the motor cleaned (especially if the bike is new to you) with electric motor cleaner. A starter that does not spin fast enough will cause the starter clutch rollers to slip. 3. The new-to-me-issue that I mentioned earlier: Make sure that the problem isn't your clutch plates sticking together. Even with the clutch lever pulled in it is possible for an older set of clutch plates to remain in contact with one-another, which causes the poor starter motor to have to try and spin the transmission along with the engine. The starter clutch will slip in this case. The immediate remedy is to roll the bike forward while pulling in the clutch lever. That will break the clutch plates free and allow the bike to be started without any problem. This issue will turn up even when the transmission is in neutral.