Need help with a weird problem may be electrical - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 9 (permalink) Old 03-21-2020, 11:35 PM Thread Starter
HarryTX
 
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Need help with a weird problem may be electrical

I have a weird problem with my '86.

It runs fine at idle, however at anything above 2,500rpm the headlight goes off and alternately bogs down then runs right then bogs down again, then runs right again etc...

I've checked everything I can think of, cleaned everything possible, scoured the forums and so on. I'm about ready to just junk it.

Anyone have a clue as to what could be the problem?

Thanks,
Harry

1986 VN750
New front tire & rear tire
Brass fuel inlets
Spline Lubed
Swing arm cleaned and lubed
Final Drive oil
Cooling system flushed and filled
Earshaved
Coastered
Mosfet R/R and relocated
AGM Battery
Stock pipes
Stock seat
Trying to achieve Anodized Red Chrome paint... from a rattle can...
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post #2 of 9 (permalink) Old 03-22-2020, 12:30 AM
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Wire problem somewhere? Junction Box?

Does it do it in neutral or only in gear and moving?

Bogging always coincides with the headlight shutting off, and above 2500rpm? If both problems only happen together, that might make it tougher to figure out.

My first thought is try the Blue Wire Mod and see if isolating the headlight helps any. Just never know what that Junction Box will do next, it's a problem child.

Have you checked the wire plugs under the neck/tank, and in the headlight shell? Might also check the plugs on the CDI, clean up any corrosion on any connections, including grounds. Bad grounds can do weird things too.

Can you watch the voltage as the problem occurs?

A lot of questions I know, but it's definitely a weird problem.

2003-21k mi
Shaved w/UniPK92+Stock Jets-TPE/MOSFET-Shinko Tires-AGM batt-bags-chrome-LEDs...more
__________________________________________________ ____________
Repair Manual: http://www.mediafire.com/file/mj7z81..._Catalogue.pdf

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post #3 of 9 (permalink) Old 03-22-2020, 12:52 AM
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You need to determine if your issue is on the hot side or the ground side. Since electrons rule the world, itís usually ground related when positive tries to pull more electrons than are available. Check your grounds inside the bullet connectors, terminal rings, etc.


1981 KZ750
1988 Vulcan VN750 (red)
2005 Vulcan VN750 (silver)
(2) 1994 Vulcan VN750 (red)

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post #4 of 9 (permalink) Old 03-22-2020, 01:53 AM Thread Starter
HarryTX
 
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I've checked and cleaned literally every connector on this thing all the way down to the stator from the taillight to the headlight. switches, buttons and Cleaned the petcock, cleaned and backblew the carbs, checked for vacuum leaks etc.

I have watched the voltage when it happens, the votage spikes to about 18v when it happens.

It only happens together, and it happens sitting in neutral and while riding.

The only thing that I haven't tried is the blue wire mod.

1986 VN750
New front tire & rear tire
Brass fuel inlets
Spline Lubed
Swing arm cleaned and lubed
Final Drive oil
Cooling system flushed and filled
Earshaved
Coastered
Mosfet R/R and relocated
AGM Battery
Stock pipes
Stock seat
Trying to achieve Anodized Red Chrome paint... from a rattle can...
HarryS is offline  
post #5 of 9 (permalink) Old 03-22-2020, 02:05 AM
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18v - Seems to point to a problem involving the R/R. Could test the R/R. Maybe the 2500rpm hits the voltage where the R/R starts to have a problem? The R/R should never allow 18v.

I know my dash voltmeter would peg to the highest reading (15v) with a loose battery cable, but the bike would start and run just fine (pure luck).

2003-21k mi
Shaved w/UniPK92+Stock Jets-TPE/MOSFET-Shinko Tires-AGM batt-bags-chrome-LEDs...more
__________________________________________________ ____________
Repair Manual: http://www.mediafire.com/file/mj7z81..._Catalogue.pdf

Owner's Manual: http://www.mediafire.com/file/nscb5f...ers+Manual.pdf
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post #6 of 9 (permalink) Old 03-22-2020, 02:40 AM Thread Starter
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I was thinking it might be the R/R since the voltage spikes like that, would that account for the headlight going out though?

1986 VN750
New front tire & rear tire
Brass fuel inlets
Spline Lubed
Swing arm cleaned and lubed
Final Drive oil
Cooling system flushed and filled
Earshaved
Coastered
Mosfet R/R and relocated
AGM Battery
Stock pipes
Stock seat
Trying to achieve Anodized Red Chrome paint... from a rattle can...
HarryS is offline  
post #7 of 9 (permalink) Old 03-22-2020, 03:19 AM
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Originally Posted by HarryS View Post
I was thinking it might be the R/R since the voltage spikes like that, would that account for the headlight going out though?

Not that I know of, a fuse is the only protection I know of for sure, and that's for amperage. There is the Reserve Lighting Unit, but I haven't seen anything about it protecting from over-volt. There's a chance it does though. I've had voltage regulators fail, put out high voltage, and pop every light bulb, had nice bright lighting for about 15 seconds.

The repair manual doesn't mention anything about over-volt protection in the RLU. It switches to the remaining bulb filament if the other fails, if low beam fails the high beam comes on but burns dimmer.

There have been reports of the headlight shutting off, but the most I recall is the Blue Wire being done and that's the end of the problem. High and low beam both work?

There's the headlight relay too, not sure what 18v would do to it. Relays can go nuts on low voltage, so maybe.

2003-21k mi
Shaved w/UniPK92+Stock Jets-TPE/MOSFET-Shinko Tires-AGM batt-bags-chrome-LEDs...more
__________________________________________________ ____________
Repair Manual: http://www.mediafire.com/file/mj7z81..._Catalogue.pdf

Owner's Manual: http://www.mediafire.com/file/nscb5f...ers+Manual.pdf
Spockster is offline  
post #8 of 9 (permalink) Old 03-22-2020, 08:33 AM Thread Starter
HarryTX
 
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Yes, both high and low beam work on the headlight. I'll take a look at the R/R I reckon.

I've had this thing for years now and it's been one flaky problem after another. When it runs, it's a great bike. But, it's had problems as much as it hasn't.

The electrical system is as quirky the personalities of the entertainment industy A-listers.

Thanks for the insights.
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1986 VN750
New front tire & rear tire
Brass fuel inlets
Spline Lubed
Swing arm cleaned and lubed
Final Drive oil
Cooling system flushed and filled
Earshaved
Coastered
Mosfet R/R and relocated
AGM Battery
Stock pipes
Stock seat
Trying to achieve Anodized Red Chrome paint... from a rattle can...
HarryS is offline  
post #9 of 9 (permalink) Old 03-22-2020, 11:20 AM
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I’d replace the VR with an ebay cheapie for $20 and see how it runs. If it works you can run it until you need a good one. Normally I’d suggest testing but the problem is intermittent and there is no win against an intermittent issue because it will say good half the time.


1981 KZ750
1988 Vulcan VN750 (red)
2005 Vulcan VN750 (silver)
(2) 1994 Vulcan VN750 (red)

Engineering solutions for the VN750 Community.
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