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newb here with power questions

coolbreeze

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Hi All
I am new to bikes and to this site (first post) ,I bought a cb750 bobbed in June 79 frame hard tailed with a 82 750f motor .

it was setup for suicide clutch and shift , that went first ,reverted back to hand clutch and foot shift , i popped in a new battery and after a little bit of persuasion i got her running !!! yippy ...

After taking it out for a few rides I noticed that it was getting harder and harder to start the bike , battery was dead , so I ran out and got a charger.

Once charged it would start no problem ,but after a few rides I would have to hook it up to the charger again , ok so this is how it's going to be :banghead:

Well, fall came around and I let her sit for a few months .. I go out to fire it up and surprisingly the battery was not dead ... well thats awesome but wtf ???

Why does my battery seem to hold a good charge but after riding it for a wile does it seem to die ?

The po told me when I got that the stator/charging system had just been replaced not to long ago ..Not that I had any idea what that was at the time or still even completely understand it ..

I want to figure it out wile I'm doing some work on it during the winter but have no idea where to start . I have no clue when it comes to electrical period .

Any and all advise would be greatly appreciated !!

thanks coolbreeze
 
Could be a couple of things.
1. Even if it's new, the battery could be bad. Especially if you bought a cheap battery from WalMart or AutoZone. Spending $100 or more on a good AGM Battery is worth it in my opinion. You can probably take it to any auto parts store and have them test it.
2. You could be not charging, or not charging enough. Get yourself a muti-meter, I use a cheap one from Harbor Freight, they are like $5, real nice ones can be pretty pricey. With the bike off on a fully charged battery it should read about 12.3-12.7 volts, start the bike and at idle it should be at about 12 volts. Then rev it up and at about 2500-3000 RPMs it should climb to about 14 volts. If the volts are not climbing when you rev it, it's not charging. If that's the case there's lots of info on the internet to trouble shoot charging issues. It could be the stator, the regulator/rectifier or even a loose wire someplace. You can get a stator rebuilt for about $80, a regulator/rectifier will run you about $100. Best to really study the charging system trouble shooting guides and really narrow down the issue rather than dumping needless $ replacing good parts.

Electrical issues can drive you crazy, but if you take your time, do a lot of reading, learn the ins and outs of the system, they can be solved.
 
I just took all my wires out my electrical box . Ugh what a rats nest but yes it had a regulator/rectifier (single unit) inside looks to be in good /fair condition but who knows .. Any way to test it by its self , off the bike ?
 
Hi. A good idea would be getting the original "green" shop manual, it shows the reg/rec checking procedure. I'll try to send a photo from mine when I get home.
But before all that, keep in mind these bikes are prone to electrical problems, the main reason being old wiring harnesses with bad contacts, which raises resistance and makes electrical components (incl. reg/rec) overheat, malfunction and eventually fail. Just as an example, once I had a bad case of overcharging (over 16 volts at the battery, which was subsequently evaporating). I replaced the reg/rec (had a spare one) and nothing. Eventually, the reason was just a bad contact at the ignition switch!

If you get an opportunity, take the whole wiring harness off (it's not as big a deal as it sounds) and check it thoroughly for bad contacts and broken insulation. These can also contribute to oxidation and rust, BTW. Solder through the main power connections.

And again, whenever experiencing ignition or charging problems, bad sparks, misfiring etc., always suspect bad wiring first! Otherwise you will spend a lot on parts you don't need or even worse, get those to fail over an over because of a problem that's somewhere else.
 
'Just as an example, once I had a bad case of overcharging (over 16 volts at the battery, which was subsequently evaporating). I replaced the reg/rec (had a spare one) and nothing. Eventually, the reason was just a bad contact at the ignition switch!'

I absolutely have to question all that. The ONLY part that can cause overcharging in any system car or bike is the regulator itself. I've rebuilt enough alts to know for SURE. You can lose a ground to have it not charge correctly but no ground at the ignition switch on these. All the other leads would fault other things before they would overcharge, trace them and see what they go to. Any open or resistance would kill charging, not increase it.

On these early first gen DOHC the most common cause of lack of charging is due to bad rotors, they go bad simply looking at them. Wiring can flaw the system too but not nearly as much as the rotor. I won't even look at the rest of the system until thoroughly satisfied the rotor is 100% good.
 
'Just as an example, once I had a bad case of overcharging (over 16 volts at the battery, which was subsequently evaporating). I replaced the reg/rec (had a spare one) and nothing. Eventually, the reason was just a bad contact at the ignition switch!'

I absolutely have to question all that. The ONLY part that can cause overcharging in any system car or bike is the regulator itself. I've rebuilt enough alts to know for SURE. You can lose a ground to have it not charge correctly but no ground at the ignition switch on these. All the other leads would fault other things before they would overcharge, trace them and see what they go to. Any open or resistance would kill charging, not increase it.

On these early first gen DOHC the most common cause of lack of charging is due to bad rotors, they go bad simply looking at them. Wiring can flaw the system too but not nearly as much as the rotor. I won't even look at the rest of the system until thoroughly satisfied the rotor is 100% good.

I understand your questioning this, I was pretty surprised too, but the new reg/rec gave 16v as well, and after I fixed the contacts at the switch (the whole connector was falling out), the voltage got back to normal. May have been a coincidence, but sure a weird one.

I'm using the same rotor for at least 16 years, (knock wood), and any charging or ignition problems always turned out to be wiring issues.
 
As promised, the reg/rec testing procedure:
3360e0f2829cf47b4c9d86175702b5c4.jpg


 
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