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Would it be because the rectifier/regulator? The owner before us replaced the old regulator/rectifier with a new one. I'm wondering how much AC does the stator/alternator outputs for 1978 GS750?
What matters is what your bike outputs now.
I'd stick my dual trace oscilloscope on the alternator outputs and know in about 3 seconds, not sure how you can do it.
Seriously why do you want a lithium battery, because everybody and their cousin tries to put one on their project?
 

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Discussion Starter #22
I see...well we were thinking of lithium battery because it is smaller and can fit directly inside the box where all the wiring harness is at (under the seat cover). The box was created by the previous owner and he didn't made any battery holder/tray for the lead acid battery. If we choose the lead acid battery route, we'll have to make something to hold the battery in place outside the box. I think we'll choose the lead acid battery route since we know that it will work on the bike while we don't know if lithium will work or not.

I have another question - the previous owner left a new rectifier but I don't know if it is also a regulator. It seems new (like not from the 80's or 90's) - is there any way we can test if the rectifier has a built in regulator as well (because it is a no brand rectifier so I cannot google the brand name)?
 

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Discussion Starter #24
It's a matter of the lithium battery replacement needing more attention to the power supply charging it.
example:

note what they say about lower voltage, if you just stuck one on your oem electrics you would cook expensive batteries.
So if we added that regulator/rectifier you showed as an example, we could use lithium? Does the stator/alternator output enough AC for the regulator/rectifier to output enough DC?
 

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So if we added that regulator/rectifier you showed as an example, we could use lithium? Does the stator/alternator output enough AC for the regulator/rectifier to output enough DC?
Likely ample power, but you still need to meter or oscilloscope test the outputs to know for sure that your coils and magnets (and carbon brush contacts are all good if it has them)

There are various levels of power cleanliness you might say
and your alternator likely outputs a lot more then 12 volts ac on many occasions

 

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Discussion Starter #26
I have a question regarding wire gauges - if the wire gauge coming out of the battery to the fuse holder and the fuse holder to the ignition switch is 14, can we use a fuse holder that has 12 gauge wire connected to it?
 

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I have a question regarding wire gauges - if the wire gauge coming out of the battery to the fuse holder and the fuse holder to the ignition switch is 14, can we use a fuse holder that has 12 gauge wire connected to it?
Yes, 12 gauge is bigger (y) wire sizes are backwards kinda like NGK spark plug heat ranges, you are good to go.
... you will not be creating any resistance power loss or heat.
 

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Discussion Starter #28
Yes, 12 gauge is bigger (y) wire sizes are backwards kinda like NGK spark plug heat ranges, you are good to go.
... you will not be creating any resistance power loss or heat.
okay, great! So we finally tried to start our bike today. Did everything for the ignition (not for the lights yet). Good news is that it seems that all of the electrical wiring for the ignition works. We can hear the starter relay clicking and I think the motor running for a few seconds. However, the bad news is that the engine still hasn’t run. We are suspecting that the old lead acid battery might be the culprit because a few days ago we checked the voltage and it was 6v. We recharged it and it managed to get about 12.18v. However, it dropped again to 12v. I guess the voltage of a 12v battery should be about 12.6v in order for it to start. The battery we used was the equivalent to the original battery, which had 128 CCA and 14Ah/10 hour, which I would have thought to be sufficient since we didn’t added any other extras for the ignition. Do you think we should use a battery with a higher CCA?

We have double checked each electrical components for the ignition switch and everything seems to be in good working order (tested using multimeter and referencing service manual). The only thing we haven’t and couldn’t check yet without the proper equipment are the contact breakers and the starter motor. When we started the motor using the kick start, it sounded like gas is going into the carburetor. It kinda sounded a toilet flush every time we press the kick start. Is that normal? We also forgot to turn on the choke when we tried to turn on the engine.
 

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I would have just walked over to the work bench, picked up a set of jumper cables and jump started it with a car battery, is there a reason you didn't try that?

( I assume you are still using a lead acid battery )
 

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"The only thing we haven’t and couldn’t check yet without the proper equipment are the contact breakers"

Do you have a good healthy spark at the spark plug? Chances are they are working.

You can use your meter to test the breaker points, they will go from no continuity when they are open to full continuity when they are closed. You can set the gap on the points using almost anything that you know is the same size as the clearance. Like cigarette papers <- Zig-Zag white cut-corners are 1 thou thick, folded once 2 thou, folded again 4 thou ;)
 

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Discussion Starter #31
"The only thing we haven’t and couldn’t check yet without the proper equipment are the contact breakers"

Do you have a good healthy spark at the spark plug? Chances are they are working.

You can use your meter to test the breaker points, they will go from no continuity when they are open to full continuity when they are closed. You can set the gap on the points using almost anything that you know is the same size as the clearance. Like cigarette papers <- Zig-Zag white cut-corners are 1 thou thick, folded once 2 thou, folded again 4 thou ;)
Ahh I see. Okay will do. Also, what is about with the sound that comes when the kick start is pumped? It kinda sounded like there is some liquid swishing everytime we kick the kick start. I wonder what is up with that?
We didn’t do the car battery jump start because our garage we were working with is not on pavement road and there was a truck blocking the passageway. We might try using a different battery with higher CCA to start the engine ;)
 

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I think you are hearing oil movement not gas.
Valves make lots of noise too when the carbs are open and the muffler is off, crankcase breather is another one to check.
 

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Discussion Starter #33
I think you are hearing oil movement not gas.
Valves make lots of noise too when the carbs are open and the muffler is off, crankcase breather is another one to check.
I see. Okay. We will try to start the bike with a car battery and jumper cables either today or in the next few days. The other problem we found is the petcock – my friend told me that when the petcock is on RES or ON, it shouldn’t leak because according to him, it should only pull out gas from the gas tank when the carburetor sucks in air. It should only let gas flow when it is on PRI. However, when we put our petcock to RES or ON, it leaks gas (not at a fast rate though). Is this normal? If not, is there a way to fix this?

Thank you for all your help!
 

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Discussion Starter #34
I see. Okay. We will try to start the bike with a car battery and jumper cables either today or in the next few days. The other problem we found is the petcock – my friend told me that when the petcock is on RES or ON, it shouldn’t leak because according to him, it should only pull out gas from the gas tank when the carburetor sucks in air. It should only let gas flow when it is on PRI. However, when we put our petcock to RES or ON, it leaks gas (not at a fast rate though). Is this normal? If not, is there a way to fix this?

Thank you for all your help!
And the leak comes from this hole (and not from elsewhere) when the petcock is set on RES or ON. We figured that gas should come out when it is on PRI but not on RES or ON...
103417
 

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Take the little star screws out and see if everything inside looks correct, you might just find dirt in it, one side is fuel, the outside space needs to be air and not sealed to atmospheric pressure
 

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Discussion Starter #38
Take the little star screws out and see if everything inside looks correct, you might just find dirt in it, one side is fuel, the outside space needs to be air and not sealed to atmospheric pressure
Is there a diagram/photo example to know if everything inside looks correct? I've never fixed a fuel cock before... :|

When you said one side is fuel, do you mean one of the the gold nipple? When you said outside space needs to be air, do you mean the other nipple (not the gold one)?
 

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Same principal as this but in miniature:



The side of the diaphragm where the spring is contains air,
the other side is like the valve in your toilet, it's sprung closed to shut off the flow of liquid until you compress the spring. It is vacuum from your intake manifold that compresses the spring and that only happens once the motor is running.
 

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The one you circled is the fuel output, the gold one made for a smaller hose is a vacuum line, only contains air or partial vacuum.
If fuel comes out the gold one you have a hole in your diaphragm. That would suck.
... not to mention pour extra raw fuel into your intake port.
 
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