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Molto Verboso
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on a traditional 5 wire P2 stator (not on a P) with a blue and black AC output lost sufficient power measured 8.5 volts at idle and 10 when revved. Replaced stator but still same voltage reading. Changed flywheel to a 1600BGM that was giving ignition trouble (maybe) and measure 10.5 at idle and 10.8 when revved. Still not enough to illuminate headlight.

Disconnected AC black and blue wires from terminal block to isolate and measure voltage. Scooter does not rev with wires disconnected maybe a ground needed? Idles but backfires and does not pick up RPM when open throttle. Connected black to terminal block will not rev out. Connect blue to terminal block revs out fine but lacking AC output above 11 volts. Any ideas? Inferior stator(s)?
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Molto Verboso
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Yep, sounds like a bad stator with that low voltage. Could try pulling it and look for broken wires or bad soldering spots. If flywheels holding a 19mm wrench all around the circle the stator can be the next culprit. Lucky its a common stator.
Did the lights just stop working?
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yes no headlight. The replacement stator is new and is putting out the same AC as the one I took out with about 4,000 miles. What is strange though on the replacement when I disconnected the AC wires from the loom and just had them free the scooter would not increase in RPM and would backfire. When connected ran fine on stand just not enough AC to power the lights.
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Do you have something loading the system down causing the low voltage? Maybe a headlight filament or something shorting to ground?
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Christopher_55934 wrote:
Do you have something loading the system down causing the low voltage? Maybe a headlight filament or something shorting to ground?
Don't know but it began with no headlight. The voltage is the same at the headlight/stator but no light. I tried measuring the voltage with the AC wires not connected the voltage was acting strange but I also could not get the engine to increase RPM with the AC wires disconnected from the loom the scooter would bog and backfire if open throttle.

Everything else is working on the DC circuits but the regulator is only putting out 4VDC with the 10VAC coming in.
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hibbert wrote:
Don't know but it began with no headlight. The voltage is the same at the headlight/stator but no light. I tried measuring the voltage with the AC wires not connected the voltage was acting strange but I also could not get the engine to increase RPM with the AC wires disconnected from the loom the scooter would bog and backfire if open throttle.

Everything else is working on the DC circuits but the regulator is only putting out 4VDC with the 10VAC coming in.
How about the voltage regulator? Could it be loading the system down causing low AC voltage.
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If he's not getting around 20V or more from the stator before it touches the regulator or other components after the regulator, the problem is from the 12v stator or flywheel.

European P stators are cheap to buy and cheaper to repair. I'll start there as other components after the stator don't matter if the stator is not supplying the right voltage out of AC wire.
⬆️    About 3 months elapsed    ⬇️
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Still cannot figure out what is wrong with the AC power. It began with a dim headlight where I discovered a terminal spade on the regulator was broken maybe due to vibration. This is where things began to unravel everything was working perfectly fine accept the headlight became dim so I began to troubleshoot and found the broken regulator.

Replaced regulator but not getting 12vac out under 8v. Thought stator was problem got new stator from India new problems with that so got new BGM stator. Same symptoms when plugged into regulator voltage drops from 12vac+ to 8vac.

With no AC output connected at regulator only INPUT AC from stator voltage is 12vac+. When AC output wire is connected to regulator with jumper from the AC input (BGM instructions) AND no OUTPUT feed the voltage drops to 8vac with no load.

DC circuits work fine although the regulator is not producing 12vdc getting 6vdc with no AC out connected to regulator and drops to 5vdc when ac out connected again with no load.

I have tried 3 new regulators, 2 BGM and one from amazon all producing same results.
broken terminal on AC output
broken terminal on AC output
AC input only from stator no AC output or DC output connected
AC input only from stator no AC output or DC output connected
AC input only from stator no AC output or DC output connected measure 12vac+
AC input only from stator no AC output or DC output connected measure 12vac+
connect AC output to regulator voltage drops to 8vac with no load connected
connect AC output to regulator voltage drops to 8vac with no load connected
connect AC output to regulator voltage drops to 8vac with no load connected
connect AC output to regulator voltage drops to 8vac with no load connected
this is the AC out which is isolated
this is the AC out which is isolated
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Engine side and with the loom disconnected what's the AC output of the stator?? If it gets up to 40V - 60V then the loom's shorting somewhere resulting in dropping the voltage...
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Thanks SaFis are you saying I should measure 40-60V at the stator output directly? I should see 40-60vac into the regulator?
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Exactly, terminals in blue & black...
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OK disconnected wires at engine measure 12vac at idle 40+ when revved.

Connect stator to loom AC INPUT only at regulator measure 12vac at idle 40+ when revved. Two wires connected on regulator ground and AC IN.

Connect AC OUTPUT (bridged/jumped) & still not connected to LOAD/loom idle voltage drops to 8vac at idle and 10vac when revved. Three wires connected at regulator ground AC IN and AC OUT which is only a loose wire not connected to anything. The 12VDC is not connected.
the is the AC output wire disconnected from regulator and not connected to the harness. Even with no load when this wire is connected to regulator voltage drops.
the is the AC output wire disconnected from regulator and not connected to the harness. Even with no load when this wire is connected to regulator voltage drops.
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Then it looks like it's the regulator that's faulty. Is this how you connect the terminals??
Forum member supplied image with no explanatory text
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Got some alligator clips and enough wire to make a testing harness outside of the scoot? Get something long enough to go from the stator to regulator over the top of the seat. That way you can isolate your harness/ individual wires from the equation.
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great idea MJRally something I haven't tested.

Tested but same. Also tested amazon regulator again also same condition although 7vac instead of 8vac with BGM.

Wire harness now eliminated as problem what else?
when AC OUT is plugged into regulator voltage drops from 12vac to 8 at idle and will not rev above 10vac.
when AC OUT is plugged into regulator voltage drops from 12vac to 8 at idle and will not rev above 10vac.
Forum member supplied image with no explanatory text
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Disconnect the kill wire from the CDI and measure again. And if you can, try a new CDI...

Also, do you maybe have a 3 pole Ducati regulator at hand??
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Thanks tested with kill wire disconnected same 12vac at idle AC IN drops to 8vac with output connected no load.

I don't have a spare CDI but could rob one if needed.
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Try one more thing. Measure the regulator's AC output without a loop...
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I'm going with inferior stator now. Is that one of the BGM Pro 2.5 stators? If so, I had terrible luck with it and it eventually fried itself.
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Thank you without loop on the AC OUT measures 0.12-0.20vac at idle and up to 0.50vac when revved. The DC OUT measures 6VDC at idle up going up to 50 when revved. AC IN from stator is up to 50vac when revved without loop.

When the loop is plugged in the AC IN/OUT drops to 8vac and revs to 10vac. The DC OUT drops to 4vdc.
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That's crazy. Can't think of anything else except the CDI that could be messing the system through the white wire since it's again a common ground to black...
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The CDI is the only part I haven't tested. All the stats seem to remain consistent after replacing 1st regulator and testing new stators/regulators/flywheels. Can't imagine that but what else to do?
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Andy, I would try a different CDI. Maybe that would also explain the revving problems you mentioned with the previous stator...
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UTC quote
Yea could be the cdi! I had lighting issues with that BGM stator and what eventually turned out to be a bad cdi. CDI internally wasn't grounding right and was using the lighting wires instead to find a ground. Had to swap it to find the error.
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