Vintage Dirt Bikes Repair Manual 1965-1978 - Volume 1 on CD

• Bultaco 125-370cc Singles, 1965-1977
• Montesa 123-360cc Singles, 1965-1975
• Ossa 125-250cc Singles, 1971-1978

Diagnosing motorcycle ills is relatively simple if you use orderly procedures and keep a few basic principles in mind.

Never assume anything. Don't overlook the obvious. If you are riding along and the bike suddenly quits, check the easiest, most accessible problem spots first. Is there gasoline in the tank?

Is the gas petcock in the ON or RESERVE position? has the spark plug wire fallen off? Check the ignition switch. Sometimes the weight of keys on a key ring may turn the ignition off suddenly.

If nothing obvious turns up in a cursory check, look a little further. Learning to recognize and describe symptoms will make repairs easier for you or a mechanic at the shop. Describe problems accurately and fully.

Saying that "it won't run" isn't the same as saying "it quit on the highway at high speed and wouldn't start", or that "it sat in my garage for three months and then wouldn't start."

Gather as many symptoms together as possible to aid in diagnosis. Note whether the engine lost power gradually or all at once, what color smoke (if any) came from the exhaust, and so on. Remember that the more complicated a machine is, the easier it is to troubleshoot because symptoms point to specific problems.

You don't need fancy equipment or complicated test gear to determine whether repairs can be attempted at home. A few simple checks could save a large repair bill and time lost while the bike sits in a dealer's service department.

On the other hand, be realistic and don't attempt repairs beyond your abilities. Service departments tend to charge heavily for putting together a disassembled engine that may have been abused.

Some won't even take on such a job - so use common sense; don't get in over your head.

Machines with batteries are also equipped with a rectifier. The rectifier serves 2 purposes. First, it converts alternating current generated by the magneto into direct current for charging the battery.

It also prevents the battery from discharging through the charging coil in the magneto when the engine is not running, or is running too slowly to charge the battery.

To test the rectifier, refer to Figure 18. Connect the test circuit shown, using the motorcycle battery and a small 6-volt lamp.

If the lamp lights with the rectifier leads connected one way, but not when the leads are reversed, the rectifier is okay. If the lamp lights when the leads are connected either way, the rectifier is shorted.

If the lamp does not light at all, the rectifier is open. Replace the magneto if the rectifier is shorted or open.

• General Information
• Troubleshooting
• Lubrication, Maintenance and Tune-up
• Engine
• Clutch and External Gearshift Linkage
• Transmission and Internal Shift Mechanism
• Fuel and Emission Systems
• Exhaust System
• Electrical System
• Wheels, Tires and Drivetrain
• Front Suspension and Steering
• Rear Suspension
• Brakes
• Body and Frame
• Wiring Diagrams

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