jwdmotorsports
jwdmotorsports Reader
4/21/09 7:18 p.m.

I'm probably about to show how little I know about motorcycles with this post.

What would keep a CB750 from charging and how expensive and involved would it be to fix?

Josh
Josh HalfDork
4/21/09 7:24 p.m.

Have the battery tested first. The PO of my bike thought it needed $400 worth of work on the charging system, but it turned out that his "new" (2 years old with a few hundred miles on it) battery didn't like being charged for a few minutes and then left sittiing for months at a time, and had prematurely given up the ghost.

RussellH
RussellH Reader
4/21/09 8:46 p.m.

From what i know about the older CB bikes, they only charge above 3000rpm or so from what I remember reading. So unless you've been running it above sustained 3000rpm I'd start there.

foxtrapper
foxtrapper SuperDork
4/22/09 4:42 a.m.

http://www.electrosport.com/technical-resources/library/diagnosis/fault-finding-guide.php

Download the guide. It's the clearest and most detailed diagnostic tool for a motorcycle charging system. It also works darn well on most cars.

jwdmotorsports
jwdmotorsports Reader
4/22/09 6:36 a.m.

This question is in regards to a bike I'm going to look at this afternoon.

That's interesting that it won't charge below 3k. I'll have to question the guy about how he's been riding it. He told me on the phone last night that he had lost the key for a couple years. He got a new key made, cleaned the carbs, and put a new battery on it. He said it runs great but won't charge.

Xceler8x
Xceler8x Dork
4/22/09 8:17 a.m.

I'd check the date on the battery. I'd also check the cables on a bike that old. The ends may have separated from the cable or they may have cracked internally leaving the insulation looking good at a glance.

Then again, the stator may be toast in which case you'll probably have to go case diving to pull and replace.

Old bikes, like old cars, are a crap shoot.

jwdmotorsports
jwdmotorsports Reader
4/22/09 8:32 a.m.

Would it be a problem to ride it about 10 miles with a charging issue? I don't own a truck and that would be the easiest way to get it home.

foxtrapper
foxtrapper SuperDork
4/22/09 12:37 p.m.

Ah, darn hard to check a charging system thoroughly without a bit of time. A multi-meter across the battery will tell you if it's working or not.

Yes, it is a problem riding 10 miles without a charge, unless the battery is in tip top shape and fully charged. Otherwise, you're likely to not finish the trip.

There's three pieces to the charging system, the regulator, the stator, and the magnetic rotor. They go bad in that order. Regulator/rectifiers go bad pretty universally. Stator windings hardly ever go bad, but old Hondas are notorious for breaking the wires coming off the stator going up to the rectifier/regulator. The magnetic rotor never goes bad.

But before blaming any of them, suspect the battery and the electrical connectors first. They frequently are corroded, and a bikes charging system will not tolerate corrosion like a cars will.

93gsxturbo
93gsxturbo Reader
4/22/09 1:48 p.m.

I would bet you could make it 10 miles on a tip top battery. There is very little electrical draw on a bike without the headlight and blinkers. If you are brave, unplug the headlight or pull the fuse, dont use the blinkers, and you will make it home.

Mental
Mental SuperDork
4/22/09 2:28 p.m.

Once you get the bike going (jump it with a car) you'll be fine.

If I was a betting man, he let the battery die completely and the batter developed a bad cell. Take measuremesnts of the batter and go to Wal-Mart and get a new one. Then go to Sears and get a trickle charger so it never happens again.

benzbaron
benzbaron Reader
4/22/09 2:45 p.m.

My buell battery tried playing the I don't want to charge game last week, I stuck in on the charger at 10A for a few hours then over night at 2A it now starts and runs. All I know is that even when the battery was completely dead I was able to pop start it. I'm stupid so 10miles doesn't sound far enough away to keep a dying bike away.

Good luck and hopefully it is a wire or ground or dead battery and not the actual charging sysem.

Xceler8x
Xceler8x Dork
4/22/09 3:40 p.m.
Mental wrote: Take measuremesnts of the batter and go to Wal-Mart and get a new one. Then go to Sears and get a trickle charger so it never happens again.

Mental has the right idea. I replaced the battery on my TL1000S like this. Wally World had the right size battery AND cranking amps. Worked great. $30 for a new one from Wal-mart. $50+ from any motorcycle dealer.

jwdmotorsports
jwdmotorsports Reader
4/22/09 8:04 p.m.

So, went to look at the bike.

Owner is convinced that it needs a stator ($285 at the local bike shop). However, I think the owners thinking is faulty and that's not the problem.

So, what I'm debating is...............

Do I spend $500ish on a bike that needs tires, charging system gone through, general cleanup and odds and ends parts or..............

Do I just cough up the money and by a decent ridable bike from the get go?

ManofFewWords
ManofFewWords Reader
4/22/09 8:12 p.m.

Lowball him if its otherwise a nice bike

Josh
Josh HalfDork
4/22/09 8:13 p.m.

Lay out the worst case scenario and use that to drive down the price. That strategy worked out DAMN well for me. I was also lucky enough to find a local battery guy that was even cheaper than Wally World. Chances are no bike that age/price is truly going to be in need of nothing. And if you are the one buying the things it needs you get the benefit of picking the parts.

jwdmotorsports
jwdmotorsports Reader
4/22/09 9:12 p.m.
ManofFewWords wrote: Lowball him if its otherwise a nice bike

It wasn't that nice. It had about 66k miles and looked like it's been sitting outside for the last two years that the owner said it's been off the road.

Mental
Mental SuperDork
4/23/09 10:14 a.m.
jwdmotorsports wrote: ...So, what I'm debating is............... Do I spend $500ish on a bike that needs tires, charging system gone through, general cleanup and odds and ends parts or.............. Do I just cough up the money and by a decent ridable bike from the get go?

I have done the first option as many times as I have done the 2nd. Tires are really not that expensive. Look around online and at smaller bike shops and you can get a good set for less than a single high performance car tire.

Even if the stator is bad, CB750s are fairly popular and I am betting you can get one on ebay or a motorcycle scrapyard pretty cheap.

You also mentioned the body is kinda ugly from being outside. That is really a can of spray paint, some chrome polish, a stack of old shirts and a good weekend's worth of elbow grease.

So, here is the litmus test; Do the bike excite you? With motorcycles that is always the bottom line. Not just the model itself, but that particular bike. CB750s are just classicaly goregeus and there is a lot you can do with them stylewise, to include leaving them be.

To be honest, it sounds like you are lukeward on this particular 750. In which case walk. But if you do like it, negotiate like you would a car, find a deal you are happy with and spent a zen-esque weekend going through the bike, and ride it with pride knowing you brought it back to life.

Any bike that runs, has a title and looks even remotely decent is worth a grand, especially in the spring. So if you get it running, you can get your money back, without even trying.

jwdmotorsports
jwdmotorsports Reader
4/23/09 11:17 a.m.
racinginc215 wrote: Pass it up and wait for something nicer. but you need this <img src="Photobucket" />

I remember that you were in my price range but you're a little too far away. You heading to the superbike race in a couple weeks down here in Birmingham?

914Driver
914Driver Dork
4/23/09 11:31 a.m.

I don't know exactly what you're looking for or where Moody is, but ....

http://bham.craigslist.org/mcy/1106085297.html

jwdmotorsports
jwdmotorsports Reader
4/23/09 7:44 p.m.

That does seem like a good price.

I was thinking something like an old Honda CB, Yamaha XS, etc. I would buy the bike from racinginc215 if he was a little closer.

4g63t
4g63t Reader
4/24/09 1:26 p.m.

Is it a SOHC CB750? www.sohc4.net Is it a DOHC CB750? www.cb1100f.net (tell them 79cb750f sent you) If DOHC it's usually the rotor.

jwdmotorsports
jwdmotorsports Reader
4/24/09 9:56 p.m.

How close are we talking?

jwdmotorsports
jwdmotorsports Reader
4/25/09 2:41 p.m.

Cool. Would definately be interested in it. $500ish?

jwdmotorsports
jwdmotorsports Reader
4/25/09 2:56 p.m.

Just to clarify. You have a title on the bike? I have to have a title in Alabama for anything 1975 or newer.

Our Preferred Partners
VGIEwEaIhzMemmgTJAj4ZdzYZRmNMCZLsEnI7Qr2DLsdExzIl6NDzTTF77QVVcDq