Low voltage, charging system questions

discussion about the 750 Sport and '89/'90 900SS, which share many mechanicals with the Paso series
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GuinnessDave
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Joined: Mon Mar 03, 2014 1:29 am
model: 750 Sport
year: 1990
Location: Savannah, Georgia, USA

Low voltage, charging system questions

Post by GuinnessDave »

So the saga continues. Finally hooked up a volt meter to battery to look at the voltage while riding. I leave the house with 13.5V and while riding it drops and remains at 14.26 or so. It occasionally does not spark, cutting out the motor for a second then it is back running again. The bike had a new regulator put on about 5-6 years ago. Connections "look" good, but, hard to say. I heard the bike is supposed to run at 14.5-15.5V. If this is true, could that be what is causing my ignition to cutout sometimes? I have new Dyna Coils and just did the relay to run battery power directly to the coils. I cannot figure out how to find why it is cutting out. I followed most all of the connections of the bike and cleaned and/or looked at them.

Any suggestions? Is there another way to more specifically check the charging system? Is there a way to check the regulator?

Thanks -Dave
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higgy
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Re: Low voltage, charging system questions

Post by higgy »

https://www.electrosport.com/media/pdf/ ... iagram.pdf

this chart and a DVOM will guide you through the charging system
Nominal voltage on these bike with a good regulator,stator and fully charged battery is 13.5 to 14.5 at 2000rpm.
at idle it may drop especially with all the lights on but not go below 12.5


anything other than this behavior indicates a problem and will cause the regulator and stator to overheat and shorten the life of both

things to check that are often overlooked :fart:
1. fuel filter
2. ignition switch,contacts and wiring at the base of the switch
3. kill switch
4. grounds everywhere
Ducati,making mechanics out of riders since 1946
There's no problem so bad that a little fixing can't make it worse! : )
If it ain't broke keep fixin it till it is
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GuinnessDave
Posts: 31
Joined: Mon Mar 03, 2014 1:29 am
model: 750 Sport
year: 1990
Location: Savannah, Georgia, USA

Re: Low voltage, charging system questions

Post by GuinnessDave »

Thanks Higgy, I'll keep trying. I idid bypass the ignition switches with a relay. Will look at kill switch and the link.
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higgy
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Re: Low voltage, charging system questions

Post by higgy »

relay mod is one good step but not always the answer. I would suggest taking the connector off at the base of the switch and check it for melting and corrosion at the terminals and connector. Voltage drop testing is also a very good idea :idea: http://www.aa1car.com/library/voltage_drop_testing.htm

Checking and cleaning of all the grounds will also get you headed in the right direction. Details are in the 750 FAQ

Checking your fuel filter to be sure it is not restricting the flow of fuel which makes the pump work harder robbing the entire bike of precious electrons causing everything to get hot. Intermittent problems are always connection issues caused by corrosion or mechanical problems at the terminals or connectors.

relay modding the headlights will also lower the electrical stress on the getting harder all the time to find ignition switch. Seems the world has finally rediscovered these very unique Ducatis and pricing is headed up. The 907 is much sought after these days followed by the sport,906 and 750.

Always,always always it is a great idea to check the F.A.Q, Almost every single topic is covered in one of the FAQ's in great detail

The search function also helps but it will take some time to figure out how to use it effectively
Ducati,making mechanics out of riders since 1946
There's no problem so bad that a little fixing can't make it worse! : )
If it ain't broke keep fixin it till it is
88 750
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92 907ie
GuinnessDave
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Joined: Mon Mar 03, 2014 1:29 am
model: 750 Sport
year: 1990
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Re: Low voltage, charging system questions

Post by GuinnessDave »

Roger all of that Higgy. I have gone through the FAQ a fair bit. I was never able to find a 750 sport wiring diagram. I believe the one I have in the manual is for the Paso. If you're talking about taking the bottom cover off the ignition switches, I did do that. Looked okay, however, we did find a voltage drop on one of the wires, it was down to 11V when the rest were at full battery charge. Thus why we tried the relay around it. The previous owner took out the fuel pump and I have dellortos on it now. It seems to run fine on gravity, full or low on fuel. Lots of stuff to read through now with all your links, which I will do. I hope it's going up in value haha, I need to get this bloody issue fixed soon so I can bring it to Barber to try and sell it. Doing a lot of this lately.:banghead: Thanks again.
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higgy
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Re: Low voltage, charging system questions

Post by higgy »

look for the wiring diagrams in the documents section both the mod and the wiring diagram are there for the 750 sport
Ducati,making mechanics out of riders since 1946
There's no problem so bad that a little fixing can't make it worse! : )
If it ain't broke keep fixin it till it is
88 750
90 906
92 907ie
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ducinthebay
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Re: Low voltage, charging system questions

Post by ducinthebay »

I'm going to guess ignition switch. See if you can replicate it while riding and wiggling your keys.

Never put more than one other key on your ring, and DO NOT lube your tumbler with graphite. (despite what the label says) The switch contacts are under the tumbler, and all that graphite will end up on your rotating contacts.

Cheers, Phil
Duc in the Bay
1990 750 Sport x2-Rosso Blanko (900ss copy) & Nuovo Nudo (Scrambler project)
1991 907 -mostly stock
2002 ST4s - Lots of mods.
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higgy
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Re: Low voltage, charging system questions

Post by higgy »

+1 ignition switch :idea:

when you took the base connector off did you look at the white contact plate it connects to ?

There is a FAQ about rebuilding the switch internally if in fact the connector fits as intended,severe cases also melt the black connector around the terminals
Of course if the pump has been removed/disconnected the filter will not cause electrical issues...only fuel issues if clogged its does need to be disconnected tho..........you do seem to have a clue :beer:
Ducati,making mechanics out of riders since 1946
There's no problem so bad that a little fixing can't make it worse! : )
If it ain't broke keep fixin it till it is
88 750
90 906
92 907ie
Mc tool
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Re: Low voltage, charging system questions

Post by Mc tool »

powering the coils via a relay is a good mod but you also need too power the digiplex the same way . When I had voltage drop issues the thing would run fine till I switched on the head light then it would die for a second , backfire ( big flames an everything ) and then carry on . As things got worse it would do it in time with the blinkers too , which was fun at the roundabout ..... not !, but it was low voltage to the digiplex and a bit of maintenance and a couple of relays sorted it :)
I wish I was young again............Id be heaps smarter than last time
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