1977 KZ750B Twin. Thought it was Carbs

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The answer is NO, a bad charging system won't affect how the bike runs until the battery discharges.  And when that happens, it's common to drop a cylinder, the headlamp goes really dim, turn signals won't flash, the electric starter won't engage, stuff like that.

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The answer is NO, a bad charging system won't affect how the bike runs until the battery discharges.  And when that happens, it's common to drop a cylinder, the headlamp goes really dim, turn signals won't flash, the electric starter won't engage, stuff like that.

Nessism I would never challenge you on a carb issue but I am going to call you out on this one if the readings stated are correct . You are right in that as long as the battery voltage is higher than the regulator output then the meter will read the higher value however, for the voltage reading to drop to 9v and then return to 13v this can only happen due to a significant load being put on the system momentarily, when you operate the starter system voltage will drop to between 9.5v and 10v. (This is one of the reasons why people fit by-pass relays) There is nothing other than the starter than can draw this big a load under normal circumstances ( nothing else has a big enough cable to carry in excess of 80amps) therefore this would suggest that the charging system is at fault (or a battery lead is chaffed through against the chassis) as this is the only circuit that isn't fused apart from the starter. The issue isn't the battery discharging as the voltage wouldn't then bounce back to normal.
I would suggest rechecking your readings as if what you have posted was correct then you are dealing with a potential fire risk (IMHO)also carefully inspect the yellow stator wires and red lead from the RR to the battery for any sign of damage or heat

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This isnt a battery drain issue. The battery has NEVER gone dead and floats at 13.5V (lithium). I think something under the tank may have gotten pinched, as it has before, and may be causing a short. Regardless, Im getting rid of the Battery Tender brand lithium battery. Though I have had mine for a few years without issue, Im no longer comfortable with it.

Im hoping this isnt a stator issue. Still no one has said what would make the bike jerk so violently, though I have asked a bunch of times. That would be helpful

 

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 Still no one has said what would make the bike jerk so violently

 

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I can’t see a 16/18 gauge wire under the tank being capable of carrying the amps needed to dead short a battery and drop voltage to 9v on a good battery.

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 Still no one has said what would make the bike jerk so violently


 

I don't think we can answer that question. Voltage too high probably would not directly impact how the engine runs. A big drop in voltage would feel like you were toggling the run/stop switch on and off. I wouldn't think this would cause the bike to buck.  It seems like it would just fall flat and then come back on, but I can't say for certain.

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I can’t see a 16/18 gauge wire under the tank being capable of carrying the amps needed to dead short a battery and drop voltage to 9v on a good battery.

I agree.  I'm not really in favor of the "voltage is dropping due to a short circuit" theory. If he's measuring the voltage directly at the battery terminals of a lithium battery, it would take a LOT of current to drop the voltage to 9V. Something somewhere would certainly be melted and probably would be destroyed.

My first thought is measurement error. Maybe the terminal wasn't clean? Maybe the meter probes weren't securely fastened? Maybe you weren't measuring directly at the battery terminals?

If it's real, as others have pointed out, a healthy battery really can't quickly drop from 14.77 to 9V, no matter what the charging system is doing.

Here is something that I've often wondered about. The newer motorcycle specific lithium batteries claim to have built in protection. The protection is intended to prevent over charging and over discharging. I think the way it works is to include an internal switch to disconnect the cells from the terminals. So if the protection were to kick in, the battery would basically disconnect itself from the motorcycle. What happens then? Are lithium-specific regulators design to run without a battery? I'm pretty sure most traditional regulators would work correctly without a battery to smooth and damp the output.  I don't know.

Anyway, I would measure it again, very carefully, and if you still see quick drops and surges in the voltage I would try a new battery.