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Discussion Starter #1
my 72 bonneville always wants to die on me at idle and i often have to rev the engine to keep it from stalling. actually it did die on me yesterday at a stop light after couple blocks from a cold start and i couldnt start it no matter what i do. then i found out that the battery didnt have a charge to get a spark.i recharge the battery and the bike lives again. i check the bike over with a volt meter today and i only get 11.23V @ 1000 RPM and barley hitting 12V @ 2500 rpm. isnt that kinda low? the bike has electronic ignition . 6V coils and NGK plugs.
 

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This is from Sparx:
"A good basic test can be done on the motorcycle without expensive equipment by turning on the headlamp and
brakelights then place a volt meter across the battery terminals, if it drops below 11 volts within a few minutes
it is faulty (a good battery should sustain 12 volts for 10 minutes)."

I would say your battery is defective.
After charging the voltage ought to be 13V +/- 1/2V.
 

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A charged battery should measure 12.6V (with the surface charge removed).

With a charged battery and your bike running at about 3000 rpm your battery voltage should rise to ideally 14.5V.
 

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Discussion Starter #4
thanks guys. im gonna take the battery out and test the charging voltage tomorrow and see what the out put is. im putting my bet on a bad battery too. 11.5V when the bike's turned on and it's ruining the ignition at idle . i hear "pop"'s from the pips due to unburnt fuel.
 

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I suspect the reg/rec is duff that is why your battery is permanently flat. One step at a time is the way to do it though and always start with a fully charged battery. At least your bike will then run for the tests.

Let us know how it goes.
 

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Discussion Starter #6
i ran some test today. battery fully charged. hook it up, turn on the key (lights on) , i got 12.40 V . as soon as i start it, it dropped to 11.4-11.9V at idle and 12.3V at 3000 RPM. so the battery is definitely weak. im gonna hook the bike on to a car battery tomorrow and see if the charging system is putting out over 14V. but right now , all things points to the battery.
 

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do you have resistor plugs or caps?

this is a common issue, with elec ignition (do you have boyer?) that it requires resistor plug or caps (not both) , otherwise I guess the system dumps all your energy into the spark and saves nothing for the battery...I had rebuilt my 71 t120, put the hi-output sparx alternator and recifier, boyer, thought I'm all modern....but kept running the battery flat...

thanks to this site I found (and it is in the boyer doc in small print) out about resistor plugs.same one you put in but with the "R"..put them in and everthing is great now...I wll run > 14 v at 3000...breaks thru 12v at around 1700rpm...
 

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Good point Bill.

Rustspot I wouldn't change the battery just yet, the fact your voltage dropped on starting your engine just shows you are not getting a charging voltage (for whatever reason).

If your battery starts at 12.4v with lights on it can't be that bad to my mind.
 

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Thinking this through and regarding what Bill has said what is the history of your bike RS.

Has it just started doing this, after being previously OK, or has it been laid up for a while?
 
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