Re: 1980 CB750F - Starting Issue Advice needed.

Posted by epfromnyc on Sep 06, 2012; 1:28pm
URL: http://vintage-and-classic-hondas.81.s1.nabble.com/1980-CB750F-Starting-Issue-Advice-needed-tp4028643p4028774.html

Okay all... here's what i found last night. Battery is delivering 12.57 volts to the starter solenoid magnetic switch. So voltage heading directly to the starter solenoid is good. All lights (front, rear, tail lamp and headlamp) are BRIGHT. Turn signals all blink and flash nicely. Headlamp low and high beam switch works nicely. I checked ground on the bike and it seems good.  I cleaned the GREEN ground wire (screwed to ignition coils mounts to the frame) and that connection is good. Ground wires all test successfully when touched with continuity checker and to the frame of the bike.

Just to make sure of ground to the frame... I attached an addition cable to the negative side of the battery and clamped it to the body (making a solid connection). So now moving on to the start run button.

1. I press the start run button and Headlamp dims (as it should) and the returns to normal brightness.
*** Voltmeter shows no current from the starter solenoid connection leading to the Starter hot lug.
There is good current going from the battery to Battery side of the starter solenoid. The first connection point of the battery should be good for current (unless wire is bad).  I checked the starter solenoid for contuinity at the moment that I press the start run button. My thinking is that I should get continuity between both leads on the starter solenoid simply because its a switch that engages and creates a connection delivering power to the actual starter.  I did NOT get any continuity from the B and M connections while holding down the start run button. I did not get any continuity from the B and M connections while checking the starter solenoid without any power to it (which I expected).

Notes: On the starter solenoid. This one is a used replacement purchased on Ebay and listed as good working order. The 30amp metal connector fuse is intact but that could have been installed for the sale.
- The orginal Starter solenoid was suspect to me since it had blown the 30amp metal connecter fuse. I had also tried a cheaper New starter solenoid which has a modern yellow plastic 30amp auto fuse mounted nicely on top but as soon as I connected it the wires on the bike started to COOK. I immediately disconnected it and it seems that the 4 prong connections might be reversed? The wires do not cook when the 4 prong adapter cable is rotated 180 degrees and connected (making the cable appear backwards based on the position of the plastic lock latch facing towards inside of the bike).


Okay so now I have 3 starter solenoids to play with... all 3 are questionable. I will need to really test them.
Obviously the brand new after market one... should work but I am not feeling good about connecting it after the experience with 4 prong plug.

- Starter Notes: The starter works and spins the motor. I jumped th starter ( by passed the starter solenoid) and it operates. Also very nice compression sounds.


Question are there other components that work to engage the starter solenoid... I know the ignition key is good (brand new), The start run button and assembly is good, check inside and connections are clean. Neutral light indicators works when bike is in neutral. Oil light comes on at the same time when key is turned to the on position.



Thanks all!