Newbie needs some help!

[zombiekillinEMT]

Hey all. Boy, am I glad to have stumbled upon this forum! I picked up my 81 CB750F in April and have been struggling to keep it going all summer! Redid the front breaks (including replacing a piston), new battery, oil change and had the carbs cleaned professionally. Now, I still have an electrical problem (the worst kind for me, I tend to be extremely dumb when it comes to circuitry).

Let me explain...
So with the new, fully charged battery, the bike will start and run just fine...for a few days. But then, the bike will die on me, sometimes even when I'm driving it. As I'm going down the road, it'll start chugging like it's out of gas. I'll pull over as it dies on me and when I try to restart, I'll get the obvious lights dimming and maybe a turn or two before it just stops turning over for me. Or, other times, I'll go out to my bike, after it worked the last time, turn it on and everything lights up, and then when I hit the starter button, I get nothing...maybe a click if I'm lucky.

I took it to my mechanic and they told me it was because I didn't tighten the positive terminal to the battery tight enough. Okay, maybe I didn't...it could happen. But then a week later, the bike died on me again. I found a wire coming from the catelytic converter had come loose. The end was all messed up so I got out my wire cutters, cut a new end and put a brand new terminal on the end of it and plugged it back in. I spoke to my mechanic over the phone who told me that having that wire unplugged could cause the same symptoms as the loose positive terminal. He also told me that this shouldn't drain the battery. Well, the bike still didn't start and I checked the voltage on my 12v battery...it was at 11.2. So I bought a charger and that's where I sit now, charging the battery AGAIN and hoping that I can at least get my bike home so I stop racking up parking tickets.

I have a feeling that the bike will start fine tomorrow but that the same problem will arise in a few days. Anyone have any idea what this could be and where I should start looking? I'm pretty new to motorcycle maintenance, but I'm eager and want to learn! Teach me, oh wise ones!

Oh, and just for kicks, here's a pic of my bike:

[ksharp]

heres your problem i had the same problem same bike and your issue is one of thoe things and one more so then the other ! YOUR MAIN PROBLEM is the router, on the right side of the bike the router is attached to the crank which u know  all u have to do is pull off the right hand side cover and check for continuity over these two slip rings, if u do then your good and its not that, after that while u have the cover off check the brushes and make sure they arnt worn down to the scrib line if they are replace. back even further and make sure you have contunity between the three yellow leads, your three phase current, and if your have cont over all of them to one another then your good and last after that your rectifer is to blame its faliling by not letting enough voltage into your batt, also make sure all your 10 amp fuse are good and there you go. the only other problem would be your batt and dont think u have over charged it becasue i had the same problem charged it and killed it back and fourth, all this u will be able to find in your clymer but what took me for a ride was the "slip rings" the hell was i suposed to know what a slip ring was my pic u wont find in the clymer lol good lick

[ksharp]

oh and welcome, these bikes are so sick, you will find lots of very helpfull people here, and your ss looks like its in some fine shape !

[zombiekillinEMT]

Thank you, ksharp! My Clymer manual is actually on its way. I can't wait to get my hands on it! I should have bought it months ago but I had a pdf of the original service manual and thought I would get by with that for a while. Boy, was I wrong! Hopefully, I'll get some free time this next week to try out what you suggested. I'll let you know if I have anymore questions!

[TOOLS1]

Welcome to the forum. You can download the manual from the forum. We have a section at the top of the page with manuals.
TOOLS

[ksharp]

i have that pdf as well unless u have a big screen tv in your garage and a computer you dont mind getting greasy as sin hooked up to it there usless lol nothing better then having that tattered looking thing in arms reach

[zombiekillinEMT]

Well said. I had one for my 78 cb350 and it was a lifesaver. Of course, it didn't save that bike from being stolen out of my yard, but nothing's perfect.

[Peterwh]

I might be being a bit thick, but in this context, what is a "router"?  Maybe I call it something else.

[shinyribs]

Router=rotor   note the pic

[ksharp]

many thanks shiny as i am either a terriable speller or a lazy typer ....

[Peterwh]

Got it, thanks

Peter

[sgtslag]

Don't know if this will help, or not, but your charging system is not working:  the bike is running off of the Battery, alone; the Battery is not being charged, so it is running down; when it gets too discharged to run the coils, and the other electrical items (lights, mostly), your bike dies -- no electrical energy left in the Battery to create a spark across the plugs, so no combustion will take place.  By the way, this is referred to as 'deep cycling' the battery:  it is not good for lead-acid batteries, and it will dramatically shorten its life.

That is the principle of what is happening with your bike.  Some finer points are as covered, already.  I would suggest checking the voltage across your Battery, when it is fully charged, and the bike is running:  it should be higher than 13 Volts [resting voltage (voltage after the vehicle has been off for 20+ minutes, and is fully charged) on a good, lead-acid battery, is 12.6 volts].  The Rectifier/Regulator can burn out/open, preventing any charge reaching the Battery.  They're nearly impossible to test, however, as the Regulator (maintains a relatively constant voltage to charge the Battery, but cannot make up for low/no voltage, only prevents it getting too high) is physically housed with the Rectifier [Alternator puts out AC, on the three yellow wires, Rectifier converts AC to DC, (+) red and (-) black wires, which then runs the bike's electrics, and charges the Battery].  Basically, the Rectifier/Regulator is a little 'black box' circuit, and there is no way to test the components within, from the external leads you have access to.  You will need to check the Rotor, the Alternator for AC output voltage (yellow wires), and then the Battery's terminals to see if the Rectifier/Regulator is charging the Battery.

Electrical circuits are actually fairly easy to troubleshoot:  divide the circuit in half, and test for a good signal, or voltage, at that point -- if present, the problem is in the latter half of the schematic, if the signal is missing, the problem is in the former half; divide whichever half of the circuit has the problem, in half again, check for the appropriate signal/voltage -- if present, the problem is in the remaining latter half, if missing, the problem is in the former, remaining half of the schematic.  Keep dividing the circuit in half, until you find the failed component.

To apply this to your bike, you could check for AC voltage on the yellow wires:  no voltage indicates the Alternator/Rotor is not working; if AC is present, then the problem is somewhere between your Battery's posts, and the Alternator's yellow wires.  At this point, the AC goes directly to the Rectifier/Regulator.  If AC is present at the (yellow) input wires, then the Rectifier/Regulator should have a DC voltage on its output wires:  if DC voltage is present, then the Rectifier/Regulator is working, but somewhere between it, and the Battery, is a problem.  That is a large area, as every electrical component is, at least indirectly, connected to the Battery, possibly through the fuse block, switches, and maybe in series with other devices -- divide the schematic in half, and measure...

Take some time to peruse the schematics, and pay attention to the color codes used for the various wires.  I use different colors of highlighter pens to mark them on photocopies of the diagrams (that way I can mess up the copies, while keeping the originals pristine).  You will need to know the wires' color codes to locate, and trace them, on the bike.

If you do not have a Digital Volt Meter (DVM), get one.  They are available from nearly every DIY box store:  Menards, Home Depot, Lowe's, Harbor Freight, etc.  They can be had, on sale, for around $5.  You need something that will measure AC/DC voltage (20 volt range is ideal for vehicles, but you can use it around the house for testing outlets, at 110/220 VAC), resistance, and a continuity test is good, too (aka, diode tester -- beeps when there is a short between the leads, indicating continuity).

Hopefully this background information will help with this problem, and potential future electrical issues.  Cheers!

[shinyribs]

ksharp wrote

many thanks shiny as i am either a terriable speller or a lazy typer ....

It happens

[zombiekillinEMT]

Thanks for the advise, sgtslag! I do have a volt meter, but not much experience using one. I'm suppose to receive my clymer manual tomorrow so hopefully I can start making sense of all of this. Funny, I'm in second semester physics lab right now and we just started going over basic circuitry. I hope that helps a little!

I did get the charged battery back in and moved my bike (yay for no more parking tickets!). I have two so I keep one charged at all times. I know this kills the life of the battery, but the bike is my only mode of transportation right now. It's suppose to be beautiful this week and I'd like to take advantage of it!

Can anyone recommend a good beginner's guide to learning electrical systems? I'll take all the help I can get...

[zombiekillinEMT]

Okay, so it took me a while, but I finally got out to check the charging system. I just want to make sure I did it right before I go out and find a new rotor.

I disconnected the battery and unplugged the alternator. After I removed the cover, I checked the resistance between the three yellow wires and got around 1-2 ohms between each. There was no reading between the wires and the case. Then, when I checked the rotor, I got a really weird reading. The numbers jumped up into the hundreds and bounced around. I'm assuming this means the rotor is shot and I need a new one?

[zombiekillinEMT]

Also, I left the rotor in the bike when I checked it. Does that make a difference?

I just called my local bike salvage and they quoted me $169 after I give them my old rotor. Is that a decent price? What would it take to rebuild my rotor?

[zombiekillinEMT]

Another thought...I've read a couple things about cleaning off the rotor. There didn't appear to be a lot of rust, but I'm sure it couldn't hurt. What do I use to clean the rotor? I'll try anything to keep from having to spend a chunk of change on new parts...

[LukeM]

In the engine is a good idea, especially if you have to spin the nut off to get it out of there.

If you want, you could use some greaseless/oilless contact cleaner to clean the brushes, and the contact surfaces.  How to tell if it's greaseless?  Spray some on your fingertips, wait for the wet stuff to dissipate, then rub your fingers together.  If it feels oily, don't use it.  If it feels dry, then spray as needed.  

If you have an ohmmeter available, you should measure between the 2 rings, as Sarge suggested.  You should get between 2 and 5 ohms.  A 'bouncing around' reading may be some dirt on the rings where your lead touches, or it might be an intermittent connection on the rotor.  If it's not in that range, it may be time to get it replaced.  $169 sounds a little steep to me.  You may have better luck at a MC junkyard.  Just make SURE they show you the resistance measurement on the rings before you buy it.  Some shops won't let you return electrical parts purchased.

Also, check the connection of the 3 yellow wires.  There should be NO burn marks or loose connections there. Some people will bypass that connector, and solder them directly across. This takes care of the connector burning problem, but makes the regulator/rectifier harder to replace.  Your choice.

Luke M

[LukeM]

If you are reasonably sure the rotor is your problem, try * this link*.

Resistance value looks about right, and should fit your bike.  Good luck.

Luke M

[zombiekillinEMT]

Okay, thanks! I tested the rings in a number of different spots, so I'm guessing the rotor is shot. The stator seemed fine though. I just wanted to make sure I wasn't crazy, this being the first time I've done something like this.

On another note...

What are possible causes of the tachometer not working? I'm assuming that maybe the cable needs to be replaced? I haven't looked into it too much yet, but I figured I should ask since I'm here. I need to replace the bulbs for both the spedo and the tach so I might as well fix that at the same time.