My 1981 Honda cb 750c drains battery every two weeks ! PLEASE HELP

[jamthebamm]

I tested  the rotor today and it was 5.4 ohm which I assume it's slightly more than standard ,the stator test looked good tho.
I also checked the starter relay and it had corrosion inside of its wire box which I don't know if it has anything to do with battery draining or charging system but I'm gonna change it regardless cause it looks nasty .
I would appreciate any sort of help .
PS the battery is brand new yuasa .

[eric moon]

Just because its a new battery doesn't mean it is good. Take it to a battery store and ask them to test it

[Re-run]

In the manuals section is a very good write-up of how to test the dohc system.
I would look at this and run the tests and see what happens.

[jamthebamm]

Eric I also have a Shorai lithium  battery and it did the same thing to it
there is also a strange thing that happened , with Shorai the charging system dose not go up more than 13.7 V at 3000rpm but with yuasa it will go more than 14v which is normal and it should , My assumption is it indicates that old charging systems don't work well with dry/lithium battery . Correct me if Im wrong !

[Re-run]

The lithium battery works fine with these bikes after a change of the regulator, at least on the sohc since it has a mechanical regulator. I would still change it with an old bike if it is stock.

Lithiums are touchy about charging and do not handle spikes well like the old lead batteries do. Run the tests outlined in the write up and you should find your issue.

[jamthebamm]

Thanks Re-run , frankly I felt like an idiot  when I saw my bike is not charging the Shorai I told myself I should have researched more about it but right now I feel happy , I guess it was a good investment .
Ok today I'm gonna run diode test on the regulator and will write the results back here .

[jamthebamm]

Well it seems the regulator is shit so i just bought a new one 'Rick's Motorsport Regulator/Rectifier 10-103'

also rotor test shows 5.6 ohm .. any comments on the rotor ?

[Re-run]

Here is that article on testing the charge system thoroughly. I had it in the wrong area.
http://www.motorcycleproject.com/motorcycle/text/DOHC_charge.swf


Rotor should be ok as long as it is under 6 ohms. Maybe recheck it to make sure though.

[sgtslag]

Re-Run, most of that fellow's techniques are good, effective, and safe.  However...

That expensive Fluke Digital Volt Meter ($100+) does not contain a fuse in its 10 Amp current circuit -- if you exceed 10 Amps (I own a similar Fluke model, been using it since 1983), not only will you destroy your meter, but you could start a fire.  I use voltage readings, not amperage readings, as voltage readings draw a few  micro-Amps through the Voltmeter's circuit, no fuse required, no fire hazard, and no shock risk at these voltages.

Anybody who wishes to follow his testing routine for amperage, needs to install an in-line 10 Amp fuse/circuit breaker, to avoid property damage (literally burning up that expensive meter), and possible personal injury (the leads, and the meter, can catch fire and cause injury, or property damage).  Have a good fire extinguisher on hand -- you should have it in your garage anyway.  

His load approach on the windings of the Stator, can be done without removing the yellow wires from the plastic connector.  All you need do is measure the AC voltage across the leads, testing all of them.  They supply AC voltage, and current, to the Rectifier, which converts it to DC, which powers the bike.

Disconnecting them can cause a surge within the wires of the Stator, which has the potential to damage, or weaken it.  Measuring the AC voltage, by inserting the Meter's leads into the back side of the connector (into the yellow wires' connectors) will give you the same AC voltage reading, using the bike as your load (no 2-ohm/100 Watt resistor needed).  If you find 0/low Volts AC, on any yellow wire, you will need to determine if the problem is in the Stator, or the load it is connected to -- the Rectifier.  The easiest, safest method, is to take resistance readings between the yellow wires (see the FSM).  If you must, you can follow his loading directions, but I recommend against it (potential surges in the Stator).

Thanks for posting his article.  He is thorough, and his methodical approach will lead you to the problem.  Cheers!

[jamthebamm]

Thanks re-run , yeh I double checked yesterday and it was 5.6 ohm . I guess the new stator will be here next week and hope resolves the problem , would love to have my lithium battery back on , everything is shinier with it