Why is my bike running?

[gbw]

77 GS750B. Has separate reg and rec. The rectifier is bad yet my bike still runs. How is that possible?

When I say my rectifier is bad what I mean is that all 6 diodes fail the forward conductivity test. They all pass the reverse non-conductivity test.

To me this says, as the AC power from the generator is sent to the rectifier, there is no path for it to travel to the battery or any other part of the bike. I've been riding this bike a lot and have not connected to the battery tender in weeks. It actually runs good but I am very confused as to why it runs at all. Any ideas?

I've ordered my replacement r/r from duaneage and am looking forward to connecting it up and then doing some plug chops...which I've put off until I get the r/r installed.

Thanks!

 

[seuadr]

mmmmmagggic?

uh, how long is it running? could it just be from battery charge?

 

[bwringer]

What's your DC voltage reading at the battery?

I'm wondering if you've done the testing incorrectly or misinterpreted the results. It's also difficult for some meters to test the rectifier diodes correctly.

A fully charged battery will run the bike and lights for a couple of hours at least, but not for weeks.

 

[gbw]

Thanks for the replies. I followed the troubleshooting procedure from the manual to determine that either the generator or rectifier was bad. The generator passed its specific test. I supposed I could have tested the rec improperly but I double/triple checked. Anyway, I didn't take notes while I was doing it, but I'll go run thru the tests again this afternoon and jot down notes to post with meter readings.

But, what I'm sensing is that if the rec is truly shot the bike should not run or charge the battery.

Hmmmm. Magic? Hmmm

Thanks...I'll post info later.

 

[trippivot]

not an alternator system like a car. remove the battery post and the engine dies. is that what you are thinking ?

as long as there is enough DC to power the ignition system it'll run.

 

[gbw]

not an alternator system like a car. remove the battery post and the engine dies. is that what you are thinking ?

as long as there is enough DC to power the ignition system it'll run.

I guess my confusion is around the question: If my rec does not have a forward continuity path, how can there be any DC voltage?

Anyway, I'll run the tests again later today when I get time, retest the rec, and post the results. I'm very confused.

 

[Steve]

When I say my rectifier is bad what I mean is that all 6 diodes fail the forward conductivity test. They all pass the reverse non-conductivity test.

Take notes on the readings and let us know what they are. You will get two different readings, so you have to be sure what you are looking at.

I'm wondering if you've done the testing incorrectly or misinterpreted the results. It's also difficult for some meters to test the rectifier diodes correctly.

Electrical work is the downfall of many mechanics. Like anything else, you have to understand the basics and then expand on them. Because you can't see electricity, it is harder to grasp just what it is that you are measuring. In the course of checking the diodes, you will be taking 12 separate measurements. Is that how many you did? Does your meter have a "diode check" function? If it does, use it. Check each diode in both directions. One direction should show about .5 volt, the other direction should show nothing. If your meter does not have a diode test function, use the resitance check function (ohms). Again, check each diode in both directions. One direction should show a relatively low reading, the other direction should show open, infinite or OL readings.

I supposed I could have tested the rec improperly but I double/triple checked.

You may have double- and triple-checked, but if you did it wrong the first time, then did it wrong again, and again, there are still no conclusive results.

I guess my confusion is around the question: If my rec does not have a forward continuity path, how can there be any DC voltage?

The bike works quite well off the voltage that is happily provided by the battery. The charging system keeps the battery charged. (Some people also view it that the charging system is what powers the vehicle, the battery is only for starting the engine to get the charging system to run. This is also correct.) Actually, the bike doesn't really care where it gets its electrical power. The 'alternator' and the battery are in parallel in the system, so the bike will draw from whichever system gives it more power.

 

[gbw]

Thanks gents. I feel like a dope.

Ran the tests again and they indicate rec is fine but reg is bad. I must have misinterpreted the original results. This makes more sense as to why the bike is still running.

When I disconnect the reg (yellow wire), and connect the wh/gr from gen to wh/rd to rec, run at 5k rpm, rec output (red) is 112VDC.

The manual suggests that 16.5VDC or over indicates good rec and gen. Last time I must have misread the manual as "16.5 or over indicates faulty reg or gen".

When I reconnect everything (including reg) and measure from battery pos to good ground, running at 5k rpm, I get 11.9VDC. According to the manual this indicates bad reg (outside the 14v to 15.5v range).

So I guess 11.9VDC is enough to fire the coils, run the lights, and charge the battery.

Now I have a follow up question: I just replaced K&N pods with stock airbox (still running stock exhaust), rejetted to stock jets, replaced original coils with new coils (these), have new wires, plug caps, and plugs. The carbs are running rich but I've been putting off plug chops and further carb tweaking until I get the new r/r. Will the new r/r make a difference or should I start plug chops and carb tweaking before I replace it?

I was a little disappointed with the spark after the new coils and everything. It seemed a little stronger than with the old coils but is still not as strong as I think it should be. Do you think having a working reg will help make the spark stronger?

Sorry to be such a pest with all these questions and really appreciate all the expertise.

 

[Steve]

Yes, a good-working regulator will make a difference in the spark. Hold off on your plug chops, etc. until you get the electrical up to snuff.

Think of it this way, the coils are just transformers with about a 2000:1 ratio.
You put 14 volts into the coil, you get 28,000 out.
You put 12 volts into the coil, you get 24,000 out.
You put 10 volts into the coil, you get 20,000 out.

No telling how much you actually need to run properly and efficiently, but in this case, the more the merrier. :dancing:

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