Topic: Bike kick starts but doesn't electric start ('74 CB750K4)

[Yoshimitsuu]

Hey all,

I ran into a strange issue on the bike when installing a new headlight. I wanted to go for an LED headlight and check the specs so that I could match it with the old Sylvania that was in the bike. However, while I was in there I checked the wiring from a wiring diagram because I knocked a few wires loose and they all checked out. The problem is with the electric starter that worked at one time but now chooses when it wants to work.

I thought that the electric starter was shot but today I charged the battery to 100% and pressed the button and it tried to turn over but did not turn on. Kick starting the bike works fine and the bike will start first kick usually.

Another thing that I noticed is that with my battery tender hooked up one press of the electric start button will knock my battery below 80% after which it will click and then trying anymore will yield nothing. It seems like the electric starter drains the battery a lot.

Any suggestions? I don't mind using the kick starter for now but I want to figure this out for the times where the electric starter would be more convenient. Thanks in advance!

TL;DR: Bike kick starts but won't electric start. At 100% charge will try to turn over but won't turn on. Seems like electric starter is draining a lot of battery charge. Looking for fix to restore my smile.

[BobR]

    Is this a new problem that occurred after you messed with the wiring? If not to me it sounds like a tired battery. Is the battery old? Starters require a lot of "juice". Bob

[Yoshimitsuu]

The problem is new after installing the headlight but I rechecked those wires and they all seem to be going to the right places. I could definitely be wrong though. The battery is a new Scorpion AGM battery that I just recently installed in July. It's a pain because it always used to start before I replaced the headlight so a part of me really thinks that it's wiring but I connected everything according to the wiring diagram.

What wires are attached to the starter button? The engine kill switch works and so does the headlight switch so really the only thing that isn't working is the electric start. Again, with a full charge is tries to start but doesn't. It always used to before.

[Yamahawk]

You need a new battery. I believe that when you kick start the bike, your voltage is high enough to fire the ignition, but when you press the start button, the voltage will drop down below 10v and it won't fire. I know this is an issue on more modern bikes, and could be your problem. I know the battery is most likely the culprit.
Charlie

[Yoshimitsuu]

I'm not sure it's the batteey. I checked the continuity with a multimeter and it read 13.5 before a start with 100% charge and then 12.5 after the button was pressed. Would a drop of 1V when starting mean needing a new battery?

Also, I bridged across the solenoid to check what the issue is and it does turn over so I'm assuming that it's not the solenoid. It's weird though it's acting like if it was the solenoid with the click but not starting.

[CycleRanger]

Is your headlight on when you're trying to use the starter?

[sixthwisconsin]

Sounds like your starter button is bad or you knocked the starter button wires loose in the bucket. I would check all those connections and be sure you are getting good contact. Use some dielectric grease while you're at it.

[Yoshimitsuu]

Im going to double check in the bucket to make sure but I'm fairly certain all are connected and accounted for. Through the few times if uninstalled and reinstalled I could have definitley knocked something loose. To be sure, I'm looking at Yellow/Red and Green/Red wires for the starter circuit as per the wiring diagram. Am I correct?

My headlight is on when I try to start it each time. If I continue to try the starter eventually it will drain the battery so much so that the turn lights won't work while the headlight is on and vice verse.

[CycleRanger]

My headlight is on when I try to start it each time. If I continue to try the starter eventually it will drain the battery so much so that the turn lights won't work while the headlight is on and vice verse.

Can you turn off the lights while you're using the starter? Your '74 should have a headlight switch.
It sounds like the lights are pulling down the voltage.
Also, even though the battery is fairly new you might have it load-tested just to be sure.
What are the specs of the battery?

[Yamahawk]

The problem is new after installing the headlight but I rechecked those wires and they all seem to be going to the right places. I could definitely be wrong though. The battery is a new Scorpion AGM battery that I just recently installed in July. It's a pain because it always used to start before I replaced the headlight so a part of me really thinks that it's wiring but I connected everything according to the wiring diagram.

What wires are attached to the starter button? The engine kill switch works and so does the headlight switch so really the only thing that isn't working is the electric start. Again, with a full charge is tries to start but doesn't. It always used to before.

I have a Scorpion battery less than a year old, and it is bad. It still gives a reading of proper voltage, but it has no AMPERAGE. This is typical of AGM batteries, when they fail, they do not give amps, just their voltage. It will not start the bike. Try changing to a lead acid type battery if you have a spare one from another bike. You might find the Scorpion AGM battery is the problem.
Charlie

[Sprocket75]

I would troubleshoot this via process of elimination. Before we start, let's go ahead and disconnect your headlight bulb. This will eliminate that from the equation so that we can test the other systems. We can reconnect it afterwards.


1- First, check the connections from the starter switch into the headlight bucket. Make sure they have good connection with no loose or cruddy solder joints. You can use electrical contact cleaner on these too. Yellow/Red is your voltage side when the button is pressed BTW.
2- Check the connection inside of the headlight bucket. Validate that you have voltage on the Yellow/Red wire there when pressed.
3- Validate that there is voltage at the Yellow/Red wire at the solenoid when the button is pressed.
4- Validate that the Green/Red wire has a solid ground at the terminal of the solenoid
5- Check your ground connection from the battery to the frame. (This is really important) 

What did you find? Are you using a test light or a volt meter? ..or both? The solenoid is pretty simple. It is basically just a relay that uses small current to switch bigger current, per se.

Do the above steps, does the starter solenoid function? Hear it click? Voltage reading at battery side of terminal when button is pressed? Voltage reading at starter side of terminal when button is pressed? Good?

Now, did the starter spin?

[Yoshimitsuu]

My headlight is on when I try to start it each time. If I continue to try the starter eventually it will drain the battery so much so that the turn lights won't work while the headlight is on and vice verse.

Can you turn off the lights while you're using the starter? Your '74 should have a headlight switch.
It sounds like the lights are pulling down the voltage.
Also, even though the battery is fairly new you might have it load-tested just to be sure.
What are the specs of the battery?

The lights are off when the I press the starter. When I try to start the bike, I hear the click at the solenoid and the lights come on while I'm holding the button. They turn off when I let go of the button.

The problem is new after installing the headlight but I rechecked those wires and they all seem to be going to the right places. I could definitely be wrong though. The battery is a new Scorpion AGM battery that I just recently installed in July. It's a pain because it always used to start before I replaced the headlight so a part of me really thinks that it's wiring but I connected everything according to the wiring diagram.

What wires are attached to the starter button? The engine kill switch works and so does the headlight switch so really the only thing that isn't working is the electric start. Again, with a full charge is tries to start but doesn't. It always used to before.

I have a Scorpion battery less than a year old, and it is bad. It still gives a reading of proper voltage, but it has no AMPERAGE. This is typical of AGM batteries, when they fail, they do not give amps, just their voltage. It will not start the bike. Try changing to a lead acid type battery if you have a spare one from another bike. You might find the Scorpion AGM battery is the problem.
Charlie

I have the old battery that I replaced from the bike with the Scorpion AGM. I'll refill it and see if that's the problem when I get home from work.

I would troubleshoot this via process of elimination. Before we start, let's go ahead and disconnect your headlight bulb. This will eliminate that from the equation so that we can test the other systems. We can reconnect it afterwards.


1- First, check the connections from the starter switch into the headlight bucket. Make sure they have good connection with no loose or cruddy solder joints. You can use electrical contact cleaner on these too. Yellow/Red is your voltage side when the button is pressed BTW.
2- Check the connection inside of the headlight bucket. Validate that you have voltage on the Yellow/Red wire there when pressed.
3- Validate that there is voltage at the Yellow/Red wire at the solenoid when the button is pressed.
4- Validate that the Green/Red wire has a solid ground at the terminal of the solenoid
5- Check your ground connection from the battery to the frame. (This is really important) 

What did you find? Are you using a test light or a volt meter? ..or both? The solenoid is pretty simple. It is basically just a relay that uses small current to switch bigger current, per se.

Do the above steps, does the starter solenoid function? Hear it click? Voltage reading at battery side of terminal when button is pressed? Voltage reading at starter side of terminal when button is pressed? Good?

Now, did the starter spin?

Thanks for this. I'm also going to try this when I get home from work and report back. It's so odd that it worked before and now it doesn't. I made more changes to the front than the back so I suspect it's something in the bucket. Should I also take a wire brush to the bullet connectors? I'm thinking that maybe the old ones are just not doing the job.

I will report back with what I find.

[CycleRanger]

The lights are off when the I press the starter. When I try to start the bike, I hear the click at the solenoid and the lights come on while I'm holding the button. They turn off when I let go of the button.

Yeah, that shouldn't happen. I would guess you have something hooked up wrong in the headlight bucket

[Yoshimitsuu]

I just wanted to report back, it was the solenoid. I replaced it with a new one ($10, unsure of reliability) and now it starts right up. Thanks for guiding me!

[Sprocket75]

Awesome! Glad it is working now. You know, the factory solenoid that you replaced is serviceable. Just so ya know.

[BobR]

 Cool! Just one of those coincidences that throw ya off track! Bob