Common Technical Issues : CB900C Custom (80-82)
BRAND : HONDA
MODEL : CB900C Custom (80-82)
CATEGORY : Street Bikes
TECHNICAL ISSUE DETAILS
The Honda CB750 and CB900 DOHC models from 79-83 had a revised field excited alternator system not that different from what you see in a modern car.
The system consists of a field rotor with brushes, a stator and a regulator/rectifier unit that rectifies the AC output coming from the stator. When the charging voltage is too high the regulator turns off the field rotor, making the charging drop in which case the regulation circuit turns the field rotor back on. This is an ongoing process.
No battery charging is typically caused by:
1) Bad rotor (rotor shorting out). Age, heat and vibration are all causes for this failure. The rotor should have a resistance between 4.2-5.0 Ohms between the slip rings. A shorted rotor winding will show a resistance between 0.3-2.5 Ohms. Our replacement part for this rotor is our ESF901
2) Bad regulator/rectifier. Often caused by a bad rotor. When the rotor fails it draws too much current for the regulation circuit to supply, causing the regulator/rectifier to fail. The OEM typically dies alongside the rotor. Our ESR210 replacement has a thermal overload circuit that prevents the regulation circuit from failure when the rotor shorts out.
3) Stator failure. Not as common, but it does happen mainly because of the age of the OEM units in these bikes. Replace with our PE-C-MH900-A igniter unit kit.
Our Fault Finding Guide will be a great help in diagnosing when you have a charging problem on these Honda four cylinders.
To test the diodes in the rectifier part of the regulator/rectifier you can use our Diode Testing Guide.
See products available for the HONDA CB900C Custom (80-82)
Technical Resources Library : : Known Issues for Other Vehicles