New owner with a ignition problem

[mung]

I just picked up a 74 CB750.  I think it has an issue with the power from the alternator to the ignition.  The battery ran down and the bike wouldn't kick start.  I charged the battery for a bit and it ran for a few minutes until the battery ran back down again.  I am guessing that the bike should run with a dead battery just on it's own power from the alternator but maybe these beasts are different.  The headlight does get brighter when the throttle is turned so that usually means the alternator is working.  So does anyone know where I should start to trouble shoot this?

A second smaller issue is that there is a small oil leak and it looks like it's coming from a notch in the top of the motor just behind the carbs.  It feels like there is a hole back there that maybe is supposed to have a breather that goes to the airbox or something?  The airbox is gone of course because it has cone filters.  I can post a picture of the area I am talking about if that helps.

Thanks in advance for any help.

[Bryanj]

Alternator is not a stand alone(like car) on the 750 it needs battery power to charge, You need to do a full charging/rectifier/regulator check as described in the Honda workshop manual--Not Haynes or Clymers

[steff750]

you should change the battery as a matter of course its a good sign that its chargeing but a battery will only give as much as its got, crap battery means crap electrics .there is a breather pipe above the carbs if there is oil coming from there could be bad news like a worn engine we need more info like is there back pressure coming from engine breather ?

[swidds]

Hi Mate,

Had same problem with mine (1972 K series). On mine the old regulator was shot, so I upgraded it to an electrix world one. http://www.electrexworld.co.uk
and http://www.slickschoppers.com/TechArticles/DOHC_Regulator_Rectifier.htm for more info. I fitted the DOHC one rather than the SOHC because it seemed easier to wire in.

Best regards,

Paul

[BigAl (Alan)]

Hi,
I have a CB750 K4, if you post some photo's myself and others can give you some advice. as suggested, your electrics will need to be tested  to eliminate cable/connector faults and component failures. Do you have a multimeter?

Alan

[Yoshi823]

Hi Mate,

Had same problem with mine (1972 K series). On mine the old regulator was shot, so I upgraded it to an electrix world one. http://www.electrexworld.co.uk
and http://www.slickschoppers.com/TechArticles/DOHC_Regulator_Rectifier.htm for more info. I fitted the DOHC one rather than the SOHC because it seemed easier to wire in.

Best regards,

Paul

Hope that you didn't throw the old regulator away? I found on several bikes that the 'points' were corroded & just required polishing up with a points file. I then reset the actuating voltage level using a variable power supply.