Help! My bike shut off on me! Wiring?

[the boy blunder]

Hey everyone,

I just got back from a 5,000 mile tour on my new 81 custom. It was amazing BUT I am having some big time problems. I know that this talented group of people might be able to point me in the right direction to helping me out. So thanks.

-1- The Big problem: my bike is completely shut off. It kept turning off on me when i was riding and now it is completely dead. Let me describe what happened.

About 3 days ago 1 out of every 4 or 5 times i would start the bike i would turn the key and nothing would happen, no lights, no started power, etc. I figured it was the battery going bad on me. Then yesterday it got way worse. I was driving home and when i would accelerate quickly (especially in 5th) the bike would skip, or misfire and i would lurch forward. it felt like it just didn't fire or something. This happened about 8/9 times. I kept driving (trying just to get home) and it got worse. At one moment, going about 50 MPH the whole bike shut off: lights, engine, etc. I slowed down and threw it into 2nd gear and when i let go of the clutch the engine kicked back in. This only got worse when I got into stop and go traffic. It kept turning off on me and i would have to re start it by throwing it into 1st. I coasted into my block and the bike shut off and will not show any signs of having an electric life.

Where should I start trying to fix this problem? I don't think it is the battery but is it the wiring? it is definitely electric right?  Any help is appreciated.

-I will wait with the second issue until i can solve this i guess.

thanks again for reading and thanks in advance for any advice.

Jordan

[TOOLS1]

Your charging system just took a big dump. The DOHC bikes are famous for doing this. Just do a search for DOHC Charging, and you will come up with at least a hundred threads on this. Also you can download the factory service manual from the home page here. It has detailed instructions on testing the charging system components.
TOOLS

[icerigger]

First things first, get your battery on a charger ASAP, you might be able to save it. Wet cells hate to be deep discharged and might not come back.

Second, as Tools said, DOHCs don't have a particularly robust charging system. The rotor is the weakest link, engine vibrations shake the windings, the insulation wears and they short out.

RTFSM (Read The Factory Service Manual) and check the voltage across the battery at 3000RPM. If you're getting 14-15V then your battery is pooched. If you get less than 13.5 check the rotor and stator. Replace them if they don't pass. If they are okay then your regulator is done.

My money's on the rotor.

[the boy blunder]

Hey Guys,

thanks for the help. Sadly I am really low on tools, etc. because i live in new York and don't have a garage.
Its been two days that the bike has been sitting. is the battery probably a lost cause or is there a way that I can save it without a charger?

I am learning this all as I go but, Icerigger, if the bike doesn't start up then i can't test the battery right? is there another way to do that? What I have learned over the past days of research, and from what you just said, is that the rotor get gunked up pretty easy on these.

Do I basically need to buy a voltage tester, take apart the rotor and test for current? If it obviously full of gunk do you think that I need to look further or If that is replaced that it might do the trick.

I know that you can't see the problem but I am just trying to size up the level of difficulty and amount of money that this might be for a real amateur. its not looking good.

thanks again,

Jordan

[icerigger]

The bike won't do anything because the battery is discharged. The longer it sits like that, the less likely you can bring it back. You won'r be able to start the bike without and fully charged battery.

The rotor and stator can be tested using an inexpensive multimeter. Both can be done without a lot of effort. First thing you need to do is the download the FSM from the home page here and read it. It details the steps for testing the charging system.

The rotor doesn't get gunked up, it shorts out and will need to be replaced or rebuilt.

From the sounds of it, you may need to enlist the help of someone who can do a little wrenching.

[the boy blunder]

Hi and thanks again,

so, just to clarify. if i remove my battery would that be enough? assuming it is a rotor problem and I do get it fixed. Basically, is there anything i can do to save the battery if i do not have a charger?

regarding the rotor, i will go pick up a multi meter and do some more research. One of the videos i watched had a rotor that was all full of gunk from being fried but i guess that is less common.

I am going to open the rotor up this weekend and see if it is a job i can actually do. always learning!

thanks again,
Jordan

[icerigger]

Yeah, you need to get hold of a charger or take it to a garage and have them charge it for you or hook it up to a car and let that charging system charge it.

[the boy blunder]

Hey everyone,

I just ran some tests and would love some advice to see if I am drawing the correct conclusions.

I opened up the Rotor/Stator and found my rotor looking pretty greasy/slimy. see the picture below.
I ran a continuity test and set my Multi to 200. I kept getting about 6.0 (too high?)

I then tested the brushes and saw continuity. I also tested the Stator but it was still attached so i followed the yellow wires to where the meet the battery, dis-attached the clip and tested the 3 yellow wires against each other. I found continuity. I then tested the yellow wires to the casing of the stator and found no continuity (good right?)

is the obvious problem here just the rotor? Is there anything else that I need to test? If i buy a new rotor and install it and there is a second problem will it ruin my new rotor?

thanks guys!

Jordan


 

[the boy blunder]

Hey all,

I would love to order the part(s) i need so any advice would really help.

thanks,

Jordan

[icerigger]

If you're getting 6 ohms through the rotor then it's good.

How was the voltage at 3500 RPM?

[the boy blunder]

I thought that a working rotor was supposed to be between 4.4 and 5.0 cold.
Does the oil around the rotor in the picture mean anything? every rotor i have looked at does not look like that.


The bike wont start so i can't test it while running.
I will jump it this week to see if its the battery. is that what you are thinking that it is?

Why did you ask about 3500? Is that when the rotor would fail if it were a bad rotor?

any other suggestions to what it could be? is it possible it is only the battery? that would be good new huh?

thanks for any and all help, I have already learned a lot.

Jordan

[shinyribs]

The charging systems on these bikes dont function at idle. They dont kick on until 2,500 + rpms. Testing them at 3-3500 rpm is just the rule of thumb.

Test the voltage at the battery with the bike off and compare that voltage to what it puts out at 3500 rpms. You want around 14-14.5 volts,best case scenario.

[icerigger]

The rotor should be 4 ohms minimum. Some aftermarket or rewinds can go as high as 6 ohms. That range is okay.

The first thing you need to do is to make sure your battery is good. It doesn't matter if the charging system is good if the battery won't hold a charge. Buy, beg or borrow a charger and charge the battery and take it off the charger and measure the voltage. Let it sit overnight. If the voltage in the morning is more than half a volt lower, you need a new one.

Put the battery in the bike and start it. Connect the voltmeter across the battery and rev up to 3500. If the voltage is in the range that Shiny mentioned, you're good to go. If not, then and only then start to worry about the charging system.

The oil on the rotor means you're getting some oil past the seal. If it's only a little, I wouldn't worry too much about it.

[the boy blunder]

Thanks guys,

I will test the battery this weekend. It is only 6 months old so I didn't think that it would have been that.
Is it possible to kill a battery so fast? I never had to jump it. Does this indicate that maybe there is something worse going on that might have caused the battery to die? (if it is the battery) It would explain why it wouldn't start sometimes but would it explain the entire engine cutting out while i was going 40 MPH?

If i were to buy a new battery and put it on and test it would it be damaged if there were something else wrong?

thanks again,

Jordan

[the boy blunder]

Is it also possible that its the wiring? I have been fixated on the charging system because of the first 2 responses but that would be a possibility still right?

anybody know a link to a good test for the wiring?

[shinyribs]

The best way to test any wiring harness is just unplug each end and check it with a meter set to ohms.

[the boy blunder]

thanks. would I set it to 20 just like for the rotor?

[epfromnyc]

BBlunder: I am in NYC as well. What tools do you need? I have a trickle charger as well. Also, read your post but didnt see what year or model you have. Mine is 1980 CB750F SS.  Definately need to do a full electrical check on that bike.

[the boy blunder]

EPNYC, i just sent you an email. lets talk and thanks.